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videodecoder: documentation cleanup
Remove some whitespace and break lines longer than 80 columns
This commit is contained in:
Thiago Santos
parent
30e9c26b72
commit
a1c3276159
1 changed files with 52 additions and 41 deletions
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@ -25,12 +25,13 @@
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/**
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* SECTION:gstvideodecoder
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* @short_description: Base class for video decoders
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* @see_also:
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* @see_also:
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*
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* This base class is for video decoders turning encoded data into raw video
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* frames.
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*
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* The GstVideoDecoder base class and derived subclasses should cooperate as follows:
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* The GstVideoDecoder base class and derived subclasses should cooperate as
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* follows:
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* <orderedlist>
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* <listitem>
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* <itemizedlist><title>Configuration</title>
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@ -46,7 +47,8 @@
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* parameters require reconfiguration.
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* </para></listitem>
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* <listitem><para>
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* Incoming data buffers are processed as needed, described in Data Processing below.
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* Incoming data buffers are processed as needed, described in Data
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* Processing below.
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* </para></listitem>
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* <listitem><para>
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* GstVideoDecoder calls @stop at end of all processing.
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@ -62,15 +64,17 @@
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* corresponding to and referred to as 'frames'.
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* </para></listitem>
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* <listitem><para>
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* Each input frame is provided in turn to the subclass' @handle_frame callback.
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* Each input frame is provided in turn to the subclass' @handle_frame
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* callback.
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* The ownership of the frame is given to the @handle_frame callback.
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* </para></listitem>
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* <listitem><para>
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* If codec processing results in decoded data, the subclass should call
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* @gst_video_decoder_finish_frame to have decoded data pushed.
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* downstream. Otherwise, the subclass must call @gst_video_decoder_drop_frame, to
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* allow the base class to do timestamp and offset tracking, and possibly to
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* requeue the frame for a later attempt in the case of reverse playback.
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* downstream. Otherwise, the subclass must call
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* @gst_video_decoder_drop_frame, to allow the base class to do timestamp
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* and offset tracking, and possibly to requeue the frame for a later
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* attempt in the case of reverse playback.
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* </para></listitem>
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* </itemizedlist>
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* </listitem>
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@ -87,20 +91,21 @@
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* <listitem>
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* <itemizedlist><title>Seeking/Flushing</title>
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* <listitem><para>
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* When the pipeline is seeked or otherwise flushed, the subclass is informed via a call
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* to its @reset callback, with the hard parameter set to true. This indicates the
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* subclass should drop any internal data queues and timestamps and prepare for a fresh
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* set of buffers to arrive for parsing and decoding.
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* When the pipeline is seeked or otherwise flushed, the subclass is
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* informed via a call to its @reset callback, with the hard parameter
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* set to true. This indicates the subclass should drop any internal data
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* queues and timestamps and prepare for a fresh set of buffers to arrive
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* for parsing and decoding.
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* </para></listitem>
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* </itemizedlist>
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* </listitem>
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* <listitem>
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* <itemizedlist><title>End Of Stream</title>
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* <listitem><para>
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* At end-of-stream, the subclass @parse function may be called some final times with the
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* at_eos parameter set to true, indicating that the element should not expect any more data
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* to be arriving, and it should parse and remaining frames and call
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* gst_video_decoder_have_frame() if possible.
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* At end-of-stream, the subclass @parse function may be called some final
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* times with the at_eos parameter set to true, indicating that the element
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* should not expect any more data to be arriving, and it should parse and
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* remaining frames and call gst_video_decoder_have_frame() if possible.
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* </para></listitem>
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* </itemizedlist>
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* </listitem>
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@ -125,26 +130,30 @@
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* should rather be left to upstream demuxer, parser or alike. This simple
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* approach caters for seeking and duration reporting using estimated input
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* bitrates. To enable it, a subclass should call
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* @gst_video_decoder_set_estimate_rate to enable handling of incoming byte-streams.
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* @gst_video_decoder_set_estimate_rate to enable handling of incoming
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* byte-streams.
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*
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* The base class provides some support for reverse playback, in particular
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* in case incoming data is not packetized or upstream does not provide
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* fragments on keyframe boundaries. However, the subclass should then be prepared
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* for the parsing and frame processing stage to occur separately (in normal
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* forward processing, the latter immediately follows the former),
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* The subclass also needs to ensure the parsing stage properly marks keyframes,
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* unless it knows the upstream elements will do so properly for incoming data.
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* fragments on keyframe boundaries. However, the subclass should then be
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* prepared for the parsing and frame processing stage to occur separately
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* (in normal forward processing, the latter immediately follows the former),
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* The subclass also needs to ensure the parsing stage properly marks
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* keyframes, unless it knows the upstream elements will do so properly for
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* incoming data.
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*
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* The bare minimum that a functional subclass needs to implement is:
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* <itemizedlist>
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* <listitem><para>Provide pad templates</para></listitem>
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* <listitem><para>
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* Inform the base class of output caps via @gst_video_decoder_set_output_state
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* Inform the base class of output caps via
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* @gst_video_decoder_set_output_state
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* </para></listitem>
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* <listitem><para>
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* Parse input data, if it is not considered packetized from upstream
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* Data will be provided to @parse which should invoke @gst_video_decoder_add_to_frame and
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* @gst_video_decoder_have_frame to separate the data belonging to each video frame.
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* Data will be provided to @parse which should invoke
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* @gst_video_decoder_add_to_frame and @gst_video_decoder_have_frame to
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* separate the data belonging to each video frame.
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* </para></listitem>
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* <listitem><para>
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* Accept data in @handle_frame and provide decoded results to
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@ -177,16 +186,17 @@
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* on whether forward or reverse playback is requested.
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*
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* Forward playback:
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* * Incoming buffer -> @parse() -> add_to_frame()/have_frame() -> handle_frame() ->
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* push downstream
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* * Incoming buffer -> @parse() -> add_to_frame()/have_frame() ->
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* handle_frame() -> push downstream
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*
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* Reverse playback is more complicated, since it involves gathering incoming data regions
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* as we loop backwards through the upstream data. The processing concept (using incoming
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* buffers as containing one frame each to simplify things) is:
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* Reverse playback is more complicated, since it involves gathering incoming
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* data regions as we loop backwards through the upstream data. The processing
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* concept (using incoming buffers as containing one frame each to simplify
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* things) is:
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*
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* Upstream data we want to play:
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* Buffer encoded order: 1 2 3 4 5 6 7 8 9 EOS
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* Keyframe flag: K K
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* Keyframe flag: K K
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* Groupings: AAAAAAA BBBBBBB CCCCCCC
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*
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* Input:
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@ -210,19 +220,20 @@
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* this:
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*
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* while (gather)
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* take head of queue and prepend to parse queue (this reverses the sequence,
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* so parse queue is 7 -> 8 -> 9)
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* take head of queue and prepend to parse queue (this reverses the
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* sequence, so parse queue is 7 -> 8 -> 9)
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*
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* Next, we process the parse queue, which now contains all un-parsed packets (including
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* any leftover ones from the previous decode section)
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* Next, we process the parse queue, which now contains all un-parsed packets
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* (including any leftover ones from the previous decode section)
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*
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* for each buffer now in the parse queue:
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* Call the subclass parse function, prepending each resulting frame to
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* the parse_gather queue. Buffers which precede the first one that
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* produces a parsed frame are retained in the parse queue for re-processing on
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* the next cycle of parsing.
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* produces a parsed frame are retained in the parse queue for
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* re-processing on the next cycle of parsing.
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*
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* The parse_gather queue now contains frame objects ready for decoding, in reverse order.
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* The parse_gather queue now contains frame objects ready for decoding,
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* in reverse order.
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* parse_gather: 9 -> 8 -> 7
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*
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* while (parse_gather)
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@ -233,8 +244,8 @@
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* Processing the decode queue results in frames with attached output buffers
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* stored in the 'output_queue' ready for outputting in reverse order.
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*
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* After we flushed the gather queue and parsed it, we add 4 to the (now empty) gather queue.
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* We get the following situation:
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* After we flushed the gather queue and parsed it, we add 4 to the (now empty)
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* gather queue. We get the following situation:
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*
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* gather queue: 4
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* decode queue: 7 8 9
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@ -262,7 +273,7 @@
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* output queue:
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*
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* gather queue: 4
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* decode queue:
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* decode queue:
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* output queue: 9 8 7 6 5
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*
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* Now output all the frames in the output queue, picking a frame from the
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@ -287,7 +298,7 @@
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* Decoded output:
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*
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* gather queue: 1
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* decode queue:
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* decode queue:
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* output queue: 4 3 2
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*
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* Leftover buffer 1 cannot be decoded and must be discarded.
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