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We got the constants for G_LITTLE_ENDIAN and G_BIG_ENDIAN the wrong way around in some docs (fixes: #572392). Also mention G_BYTE_ORDER in the audio types section.
634 lines
20 KiB
Text
634 lines
20 KiB
Text
MIME types in GStreamer
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What is a MIME type ?
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=====================
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A MIME type is a combination of two (short) strings (words)---the content type
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and the content subtype. Content types are broad categories used for describing
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almost all types of files: video, audio, text, and application are common
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content types. The subtype further breaks the content type down into a more
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specific type description, for example 'application/ogg', 'audio/raw',
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'video/mpeg', or 'text/plain'.
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So the content type and subtype make up a pair that describes the type of
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information contained in a file. In multimedia processing, MIME types are used
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to describe the type of information carried by a media stream. In GStreamer, we
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use MIME types in the same way, to identify the types of information that are
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allowed to pass between GStreamer elements. The MIME type is part of a GstCaps
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object that describes a media stream. Besides a MIME type, a GstCaps object also
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contains a name and some stream properties (GstProps, which hold combinations of
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key/value pairs).
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An example of a MIME type is 'video/mpeg'. A corresponding GstCaps could be
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created using code:
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GstCaps *caps = gst_caps_new_simple ("video/mpeg",
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"width", G_TYPE_INT, 384,
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"height", G_TYPE_INT, 288,
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NULL);
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MIME types and their corresponding properties are of major importance in
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GStreamer for uniquely identifying media streams. Therefore, we define them
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per media type. All GStreamer plugins should keep to this definition.
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Official MIME media types are assigned by the IANA. Current assignments are at
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http://www.iana.org/assignments/media-types/.
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The problems
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============
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Some streams may have MIME types or GstCaps that do not fully describe the
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stream. In most cases, this is not a problem, though. For example, if a stream
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contains Ogg/Vorbis data (which is of type 'application/ogg'), we don't need to
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know the samplerate of the raw audio stream, since we can't play the encoded
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audio anyway. The samplerate is, however, important for raw audio, so a decoder
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would need to retrieve the samplerate from the Ogg/Vorbis stream headers (the
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headers are part of the bytestream) in order to pass it on in the GstCaps that
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belongs to the decoded audio (which becomes a type like 'audio/raw'). However,
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other plugins might want to know such properties, even for compressed streams.
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One such example is an AVI muxer, which does want to know the samplerate of an
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audio stream, even when it is compressed.
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Another problem is that many media types can be defined in multiple ways. For
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example, MJPEG video can be defined as 'video/jpeg', 'video/mjpeg',
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'image/jpeg', 'video/x-msvideo' with a compression of (fourcc) MJPG, etc.
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None of these is really official, since there isn't an official mimetype
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for encoded MJPEG video.
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The main focus of this document is to propose a standardized set of MIME types
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and properties that will be used by the GStreamer plugins.
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Different types of streams
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==========================
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There are several types of media streams. The most important distinction will be
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container formats, audio codecs and video codecs. Container formats are
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bytestreams that contain one or more substreams inside it, and don't provide any
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direct media data itself. Examples are Quicktime, AVI or MPEG System Stream.
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They mostly contain of a set of headers that define the media streams that are
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packed inside the container, along with the media data itself.
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Video codecs and audio codecs describe encoded audio or video data. Examples are
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MPEG-1 video, DivX video, MPEG-1 layer 3 (MP3) audio or Ogg/Vorbis audio.
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Actually, Ogg is a container format too (for Vorbis audio), but these are
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usually used in conjunction with each other.
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Finally, there are the somewhat obvious (but not commonly encountered as files)
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raw data formats.
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Container formats
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-----------------
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1 - AVI (Microsoft RIFF/AVI)
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MIME type: video/x-msvideo
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Properties:
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Parser: avidemux, ffdemux_avi
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Formatter: avimux
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2 - Quicktime (Apple)
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MIME type: video/quicktime
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Properties:
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Parser: qtdemux
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Formatter:
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3 - MPEG (MPEG LA)
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MIME type: video/mpeg
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Properties: 'systemstream' = TRUE (BOOLEAN)
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Parser: mpegdemux, ffdemux_mpeg (PS), ffdemux_mpegts (TS), dvddemux
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Formatter: mplex
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4 - ASF (Microsoft)
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MIME type: video/x-ms-asf
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Properties:
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Parser: asfdemux, ffdemux_asf
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Formatter: asfmux
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5 - WAV (Microsoft RIFF/WAV)
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MIME type: audio/x-wav
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Properties:
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Parser: wavparse, ffdemux_wav
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Formatter: wavenc
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6 - RealMedia (Real)
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MIME type: application/vnd.rn-realmedia
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Properties: 'systemstream' = TRUE (BOOLEAN)
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Parser: rmdemux, ffdemux_rm
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Formatter:
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7 - DV (Digital Video)
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MIME type: video/x-dv
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Properties: 'systemstream' = TRUE (BOOLEAN)
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Parser: gst1394, ffdemux_dv
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Formatter:
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8 - Ogg (Xiph)
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MIME type: application/ogg
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Properties:
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Parser: oggdemux
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Formatter: oggmux
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9 - Matroska
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MIME type: video/x-mkv
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Properties:
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Parser: matroskademux, ffdemux_matroska
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Formatter: matroskamux
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10 - Shockwave (Macromedia)
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MIME type: application/x-shockwave-flash
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Properties:
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Parser: swfdec, ffdemux_swf
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Formatter:
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11 - AU audio (Sun)
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MIME type: audio/x-au
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Properties:
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Parser: auparse, ffdemux_au
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Formatter:
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12 - Mod audio
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MIME type: audio/x-mod
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Properties:
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Parser: modplug, mikmod
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Formatter:
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13 - FLX video
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MIME type: video/x-fli
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Properties:
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Parser: flxdec
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Formatter:
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14 - Monkeyaudio
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MIME type: application/x-ape
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Properties:
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Parser:
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Formatter:
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15 - AIFF audio
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MIME type: audio/x-aiff
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Properties:
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Parser:
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Formatter:
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16 - SID audio
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MIME type: audio/x-sid
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Properties:
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Parser: siddec
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Formatter:
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Please note that we try to keep these MIME types as similar as possible to the
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MIME types used as standards in Gnome (Gnome-VFS/Nautilus) and KDE
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(Konqueror). Both will (in future) stick to a shared-mime-info database that
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is hosted on freedesktop.org, and bases itself on IANA.
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Also, there is a very thin line between audio codecs and audio containers
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(take mp3 vs. sid, etc.). This is just a per-case thing right now and needs to
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be documented further.
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Video codecs
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------------
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For convenience, the fourcc codes used in the AVI container format will be
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listed along with the MIME type and optional properties.
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Optional properties for all video formats are the following:
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width = 1 - MAXINT (INT)
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height = 1 - MAXINT (INT)
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pixel_width = 1 - MAXINT (INT, with pixel_height forms aspect ratio)
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pixel_height = 1 - MAXINT (INT, with pixel_width forms aspect ratio)
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framerate = 0 - MAXFLOAT (FLOAT)
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1 - MPEG-1, -2 and -4 video (ISO/LA MPEG)
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MIME type: video/mpeg
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Properties: systemstream = FALSE (BOOLEAN)
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mpegversion = 1/2/4 (INT)
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Known fourccs: MPEG, MPGI
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Encoder: mpeg1enc, mpeg2enc
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Decoder: mpeg1dec, mpeg2dec, mpeg2subt
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2 - DivX 3.x, 4.x and 5.x video (divx.com)
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MIME type: video/x-divx
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Properties:
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Optional properties: divxversion = 3/4/5 (INT)
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Known fourccs: DIV3, DIV4, DIV5, DIVX, DX50, DIVX, divx
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Encoder: divxenc
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Decoder: divxdec, ffdec_mpeg4
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3 - Microsoft MPEG 4.1, 4.2 and 4.3
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MIME type: video/x-msmpeg
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Properties:
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Optional properties: msmpegversion = 41/42/43 (INT)
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Known fourccs: MPG4, MP42, MP43
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Encoder: ffenc_msmpeg4, ffenc_msmpeg4v1, ffenc_msmpeg4v2
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Decoder: ffdec_msmpeg4, ffdec_msmpeg4v1, ffdec_msmpeg4v2
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4 - Motion-JPEG (official and extended)
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MIME type: video/x-jpeg
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Properties:
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Known fourccs: MJPG (YUY2 MJPEG), JPEG (any), PIXL (Pinnacle/Miro), VIXL
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Encoder: jpegenc
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Decoder: jpegdec, ffdec_mjpeg
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5 - Sorensen (Quicktime - SVQ1/SVQ3)
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MIME types: video/x-svq
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Properties: svqversion = 1/3 (INT)
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Encoder:
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Decoder: ffdec_svq1, ffdec_svq3
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6 - H263 and related codecs
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MIME type: video/x-h263
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Properties:
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Known fourccs: H263/h263, i263, L263, M263/m263, s263, x263, VDOW, VIVO
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Encoder: ffenc_h263, ffenc_h263p
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Decoder: ffdec_h263, ffdec_h263i
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7 - RealVideo (Real)
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MIME type: video/x-pn-realvideo
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Properties: rmversion = "1"/"2"/"3"/"4" (INT)
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Known fourccs: RV10, RV20, RV30, RV40
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Encoder: ffenc_rv10
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Decoder: ffdec_rv10, ffdec_rv20
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8 - Digital Video (DV)
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MIME type: video/x-dv
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Properties: systemstream = FALSE (BOOLEAN)
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Known fourccs: DVSD/dvsd (SDTV), dvhd (HDTV), dvsl (SDTV LongPlay)
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Encoder: ffenc_dvvideo
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Decoder: dvdec, ffdec_dvvideo
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9 - Windows Media Video 1, 2 and 3 (WMV)
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MIME type: video/x-wmv
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Properties: wmvversion = 1/2/3 (INT)
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Encoder: ffenc_wmv1, ffenc_wmv2, none
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Decoder: ffdec_wmv1, ffdec_wmv2, none
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10 - XviD (xvid.org)
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MIME type: video/x-xvid
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Properties:
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Known fourccs: xvid, XVID
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Encoder: xvidenc
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Decoder: xviddec, ffdec_mpeg4
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11 - 3IVX (3ivx.org)
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MIME type: video/x-3ivx
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Properties:
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Known fourccs: 3IV0, 3IV1, 3IV2
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Encoder:
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Decoder:
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12 - Ogg/Tarkin (Xiph)
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MIME type: video/x-tarkin
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Properties:
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Encoder:
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Decoder:
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13 - VP3
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MIME type: video/x-vp3
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Properties:
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Encoder:
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Decoder: ffdec_vp3
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14 - Ogg/Theora (Xiph, VP3-like)
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MIME type: video/x-theora
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Properties:
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Encoder: theoraenc
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Decoder: theoradec, ffdec_theora
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This is the raw stream that comes out of an ogg file.
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15 - Huffyuv
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MIME type: video/x-huffyuv
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Properties:
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Known fourccs: HFYU
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Encoder:
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Decoder: ffdec_hfyu
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16 - FF Video 1 (FFMPEG)
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MIME type: video/x-ffv
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Properties: ffvversion = 1 (INT)
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Encoder:
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Decoder: ffdec_ffv1
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17 - H264
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MIME type: video/x-h264
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Properties:
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Known fourccs: VSSH
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Encoder:
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Decoder: ffdec_h264
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18 - Indeo 3 (Intel)
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MIME type: video/x-indeo
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Properties: indeoversion = 3 (INT)
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Encoder:
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Decoder: ffdec_indeo3
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19 - Portable Network Graphics (PNG)
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MIME type: video/x-png
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Properties:
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Encoder: pngenc
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Decoder: pngdec, gdkpixbufdec
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20 - Cinepak
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MIME type: video/x-cinepak
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Properties:
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Encoder:
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Decoder: ffdec_cinepak
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TODO: subsampling information for YUV?
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TODO: colorspace identifications for MJPEG? How?
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TODO: how to distinguish MJPEG-A/B (Quicktime) and lossless JPEG?
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TODO: divx4/divx5/xvid/3ivx/mpeg-4 - how to make them overlap? (all
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ISO MPEG-4 compatible)
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3c) Audio Codecs
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----------------
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For convenience, the two-byte hexcodes (as used for identification in AVI files)
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are also given.
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Properties for all audio formats include the following:
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rate = 1 - MAXINT (INT, sampling rate)
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channels = 1 - MAXINT (INT, number of audio channels)
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1 - Alaw Raw Audio
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MIME type: audio/x-alaw
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Properties:
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Encoder: alawenc
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Decoder: alawdec
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2 - Mulaw Raw Audio
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MIME type: audio/x-mulaw
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Properties:
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Encoder: mulawenc
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Decoder: mulawdec
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3 - MPEG-1 layer 1/2/3 audio
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MIME type: audio/mpeg
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Properties: mpegversion = 1 (INT)
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layer = 1/2/3 (INT)
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Encoder: lame, ffdec_mp3
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Decoder: mad
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4 - Ogg/Vorbis
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MIME type: audio/x-vorbis
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Encoder: rawvorbisenc (vorbisenc does rawvorbisenc+oggmux)
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Decoder: vorbisdec
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5 - Windows Media Audio 1, 2 and 3 (WMA)
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MIME type: audio/x-wma
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Properties: wmaversion = 1/2/3 (INT)
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Encoder:
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Decoder: ffdec_wmav1, ffdec_wmav2, none
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6 - AC3
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MIME type: audio/x-ac3
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Properties:
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Encoder: ffenc_ac3
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Decoder: a52dec, ac3parse
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7 - FLAC (Free Lossless Audio Codec)
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MIME type: audio/x-flac
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Properties:
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Encoder: flacenc
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Decoder: flacdec, ffdec_flac
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8 - MACE 3/6 (Quicktime audio)
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MIME type: audio/x-mace
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Properties: maceversion = 3/6 (INT)
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Encoder:
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Decoder: ffdec_mace3, ffdec_mace6
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9 - MPEG-4 AAC
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MIME type: audio/mpeg
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Properties: mpegversion = 4 (INT)
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Encoder: faac
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Decoder: faad
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10 - (IMA) ADPCM (Quicktime/WAV/Microsoft/4XM)
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MIME type: audio/x-adpcm
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Properties: layout = "quicktime"/"wav"/"microsoft"/"4xm"/"g721"/"g722"/"g723_3"/"g723_5" (STRING)
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Encoder: ffenc_adpcm_ima_[qt/wav/dk3/dk4/ws/smjpeg], ffenc_adpcm_[ms/4xm/xa/adx/ea]
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Decoder: ffdec_adpcm_ima_[qt/wav/dk3/dk4/ws/smjpeg], ffdec_adpcm_[ms/4xm/xa/adx/ea]
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Note: The difference between each of these four PCM formats is the number
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of samples packed together per channel. For WAV, for example, each
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sample is 4 bit, and 8 samples are packed together per channel in the
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bytestream. For the others, refer to technical documentation. We
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probably want to distinguish these differently, but I don't know how,
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yet.
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11 - RealAudio (Real)
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MIME type: audio/x-pn-realaudio
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Properties: raversion ="1"/"2" (INT)
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Known fourccs: 14_4, 28_8
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Encoder:
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Decoder: ffdec_real_144 / ffdec_real_288
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12 - DV Audio
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MIME type: audio/x-dv
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Properties:
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Encoder:
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Decoder:
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13 - GSM Audio
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MIME type: audio/x-gsm
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Properties:
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Encoder: gsmenc, rtpgsmenc
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Decoder: gsmdec, rtpgsmparse
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14 - Speex audio
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MIME type: audio/x-speex
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Properties:
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Encoder: speexenc
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Decoder: speexdec
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15 - QDM2
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MIME type: audio/x-qdm2
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Properties:
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16 - Sony ATRAC4 (detected inside realmedia and wave/avi streams, nothing to decode it yet)
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MIME type: audio/x-vnd.sony.atrac3
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Properties:
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Encoder:
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Decoder:
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17 - Ensoniq PARIS audio
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MIME type: audio/x-paris
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Properties:
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Encoder:
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Decoder:
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18 - Amiga IFF / SVX8 / SV16 audio
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MIME type: audio/x-svx
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Properties:
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Encoder:
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Decoder:
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19 - Sphere NIST audio
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MIME type: audio/x-nist
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Properties:
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Encoder:
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Decoder:
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20 - Sound Blaster VOC audio
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MIME type: audio/x-voc
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Properties:
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Encoder:
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Decoder:
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21 - Berkeley/IRCAM/CARL audio
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MIME type: audio/x-ircam
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Properties:
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Encoder:
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Decoder:
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22 - Sonic Foundry's 64 bit RIFF/WAV
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MIME type: audio/x-w64
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Properties:
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Encoder:
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Decoder:
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TODO: adpcm/dv needs confirmation from someone with knowledge...
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Raw formats
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-----------
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Raw formats contain unencoded, raw media information. These are rather rare from
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an end user point of view since raw media files have historically been
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prohibitively large ... hence the multitude of encoding formats.
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Raw video formats require the following common properties, in addition to
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format-specific properties:
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width = 1 - MAXINT (INT)
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height = 1 - MAXINT (INT)
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1 - Raw Video (YUV/YCbCr)
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MIME type: video/x-raw-yuv
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Properties: 'format' = 'XXXX' (fourcc)
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Known fourccs: YUY2, I420, Y41P, YVYU, UYVY, etc.
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Properties:
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Some raw video formats have implicit alignment rules. We should discuss this
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more. Also, some formats have multiple fourccs (e.g. IYUV/I420 or
|
|
YUY2/YUYV). For each of these, we only use one (e.g. I420 and YUY2).
|
|
|
|
Currently recognized formats:
|
|
|
|
YUY2: packed, Y-U-Y-V order, U/V hor 2x subsampled (YUV-4:2:2, 16 bpp)
|
|
YVYU: packed, Y-V-Y-U order, U/V hor 2x subsampled (YUV-4:2:2, 16 bpp)
|
|
UYVY: packed, U-Y-V-Y order, U/V hor 2x subsampled (YUV-4:2:2, 16 bpp)
|
|
Y41P: packed, UYVYUYVYYYYY order, U/V hor 4x subsampled (YUV-4:1:1, 12 bpp)
|
|
IUY2: packed, U-Y-V order, not subsampled (YUV-1:1:1, 24 bpp)
|
|
|
|
Y42B: planar, Y-U-V order, U/V hor 2x subsampled (YUV-4:2:2, 16 bpp)
|
|
YV12: planar, Y-V-U order, U/V hor+ver 2x subsampled (YUV-4:2:0, 12 bpp)
|
|
I420: planar, Y-U-V order, U/V hor+ver 2x subsampled (YUV-4:2:0, 12 bpp)
|
|
Y41B: planar, Y-U-V order, U/V hor 4x subsampled (YUV-4:1:1, 12bpp)
|
|
YUV9: planar, Y-U-V order, U/V hor+ver 4x subsampled (YUV-4:1:0, 9bpp)
|
|
YVU9: planar, Y-V-U order, U/V hor+ver 4x subsampled (YUV-4:1:0, 9bpp)
|
|
|
|
Y800: one-plane (Y-only, YUV-4:0:0, 8bpp)
|
|
|
|
See http://www.fourcc.org/ for more information.
|
|
|
|
Note: YUV-4:4:4 (both planar and packed, in multiple orders) are missing.
|
|
|
|
2 - Raw video (RGB)
|
|
MIME type: video/x-raw-rgb
|
|
Properties: endianness = 1234/4321 (INT) <- use G_LITTLE_ENDIAN/G_BIG_ENDIAN
|
|
depth = 15/16/24 (INT, color depth)
|
|
bpp = 16/24/32 (INT, bits used to store each pixel)
|
|
red_mask = bitmask (0x..) (INT)
|
|
green_mask = bitmask (0x..) (INT)
|
|
blue_mask = bitmask (0x..) (INT)
|
|
|
|
24 and 32 bit RGB should always be specified as big endian, since any little
|
|
endian format can be transformed into big endian by rearranging the color
|
|
masks. 15 and 16 bit formats should generally have the same byte order as
|
|
the CPU.
|
|
|
|
Color masks are interpreted by loading 'bpp' number of bits using the given
|
|
'endianness', and masking and shifting by each color mask. Loading a 24-bit
|
|
value cannot be done directly, but one can perform an equivalent operation.
|
|
|
|
Examples:
|
|
msb .. lsb
|
|
- memory: RRRRRRRR GGGGGGGG BBBBBBBB RRRRRRRR GGGGGGGG ...
|
|
bpp = 24
|
|
depth = 24
|
|
endianness = 4321 (G_BIG_ENDIAN)
|
|
red_mask = 0xff0000
|
|
green_mask = 0x00ff00
|
|
blue_mask = 0x0000ff
|
|
|
|
- memory: xRRRRRGG GGGBBBBB xRRRRRGG GGGBBBBB xRRRRRGG ...
|
|
bpp = 16
|
|
depth = 15
|
|
endianness = 4321 (G_BIG_ENDIAN)
|
|
red_mask = 0x7c00
|
|
green_mask = 0x03e0
|
|
blue_mask = 0x003f
|
|
|
|
- memory: GGGBBBBB xRRRRRGG GGGBBBBB xRRRRRGG GGGBBBBB ...
|
|
bpp = 16
|
|
depth = 15
|
|
endianness = 1234 (G_LITTLE_ENDIAN)
|
|
red_mask = 0x7c00
|
|
green_mask = 0x03e0
|
|
blue_mask = 0x003f
|
|
|
|
The raw audio formats require the following common properties, in addition to
|
|
format-specific properties:
|
|
|
|
rate = 1 - MAXINT (INT, sampling rate)
|
|
channels = 1 - MAXINT (INT, number of audio channels)
|
|
endianness = 1234/4321 (INT) <- use G_LITTLE_ENDIAN/G_BIG_ENDIAN/G_BYTE_ORDER
|
|
|
|
3 - Raw audio (integer format)
|
|
MIME type: audio/x-raw-int
|
|
properties: width = 8/16/24/32 (INT, bits used to store each sample)
|
|
depth = 8 - 32 (INT, bits actually used per sample)
|
|
signed = TRUE/FALSE (BOOLEAN)
|
|
|
|
4 - Raw audio (floating point format)
|
|
MIME type: audio/x-raw-float
|
|
Properties: width = 32/64 (INT)
|
|
buffer-frames: number of audio frames per buffer, 0=undefined
|
|
|
|
Plugin Guidelines
|
|
=================
|
|
|
|
So, a short bit on what plugins should do. Above, I've stated that audio
|
|
properties like 'channels' and 'rate' or video properties like 'width' and
|
|
'height' are all optional. This doesn't mean you can just simply omit them and
|
|
everything will still work!
|
|
|
|
An example is the best way to explain all this. AVI needs the width, height,
|
|
rate and channels for the AVI header. So if these properties are missing, the
|
|
avimux element cannot properly create the AVI header. On the other hand, MPEG
|
|
doesn't have such properties in its header, so the mpegdemux element would need
|
|
to parse the separate streams in order to find them out. We don't want that
|
|
either, because a plugin only does one job. So normally, mpegdemux and avimux
|
|
wouldn't allow transcoding. To solve this problem, there are stream parser
|
|
elements (such as mpegaudioparse, ac3parse and mpeg1videoparse).
|
|
|
|
Conclusions to draw from here: a plugin gives info it can provide as seen from
|
|
its own task/job. If it can't, other elements might still need it and a stream
|
|
parser needs to be written if it doesn't already exist.
|
|
|
|
On properties that can be described by one of these (properties such as 'width',
|
|
'height', 'fps', etc.): they're forbidden and should be handled using filtered
|
|
caps.
|
|
|
|
Status of this document
|
|
=======================
|
|
|
|
Not all plugins strictly follow these guidelines yet, but these are the official
|
|
types. Plugins not following these specs either use extensions that should be
|
|
documented, or are buggy (and should be fixed).
|
|
|
|
Blame Ronald Bultje <rbultje@ronald.bitfreak.net> aka BBB for any mistakes in
|
|
this document.
|