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qtdemux: Don't emit GstSegment correcting start time when in MSE mode

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When using qtdemux in a pipeline that should only work as a pure demuxer (not
for actual playback), qtdemux shouldn't emit new GstSegments to correct
the start time (jump to the future) to ensure that the user experiences no
playback delay. By doing so, it's generating the wrong segments when an append
of data from the past happens. When that happens, downstream elements such as
parsers (eg: aacparse) may clip those buffers laying before the GstSegment and
create problems on the GStreamer client app (eg: WebKit).

Getting buffers clipped out because of the wrong GstSegments started becoming
a problen when this commit was introduced:

ab6e49e9cc audioparsers: add back segment clipping to parsers that have lost it

This clipping makes test DASH shaka 35 from MVT tests[1] to fail in
WebKitGTK/WPE (at least) and can potentially cause a number of other problems
in the WebKit Media Source Extensions (MSE) code.

Note that this new behaviour of not emitting new GstSegments only makes sense
when qtdemux is being used as a pure demuxer and not as part of a regular
pipeline. This is why the variant field has been added. When equal to
VARIANT_MSE_BYTESTREAM, it will make qtdemux behave differently in push mode,
taking decisions that meet the expectations for an MSE-like processing mode.
This kind of tweaks have been done in the past for MSS streams, for instance.
That code has been refactored to use VARIANT_MSS_FRAGMENTED now, instead of
its own dedicated boolean flag.

Co-authored by: Alicia Boya García <ntrrgc@gmail.com>

...who suggested to use "variant: mse-bytestream" in the caps to identify that
mode, as proposed in her unmerged patch:

https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/issues/467

[1] https://github.com/rdkcentral/mvt

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3995>
This commit is contained in:
Enrique Ocaña González 2023-02-01 12:09:52 +01:00 committed by GStreamer Marge Bot
parent e3674a3e42
commit eb5e90905c
2 changed files with 27 additions and 13 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

22
subprojects/gst-plugins-good/gst/isomp4/qtdemux.c
View file

@ -1887,12 +1887,16 @@ gst_qtdemux_setcaps (GstQTDemux * demux, GstCaps * caps)
structure = gst_caps_get_structure (caps, 0);
variant = gst_structure_get_string (structure, "variant");
if (variant && strcmp (variant, "mse-bytestream") == 0) {
demux->variant = VARIANT_MSE_BYTESTREAM;
}
if (variant && strcmp (variant, "mss-fragmented") == 0) {
QtDemuxStream *stream;
const GValue *value;
demux->fragmented = TRUE;
demux->mss_mode = TRUE;
demux->variant = VARIANT_MSS_FRAGMENTED;
if (QTDEMUX_N_STREAMS (demux) > 1) {
/* can't do this, we can only renegotiate for another mss format */
@ -1963,8 +1967,6 @@ gst_qtdemux_setcaps (GstQTDemux * demux, GstCaps * caps)
}
}
gst_caps_replace (&demux->media_caps, (GstCaps *) mediacaps);
} else {
demux->mss_mode = FALSE;
}
return TRUE;
@ -2053,7 +2055,7 @@ gst_qtdemux_reset (GstQTDemux * qtdemux, gboolean hard)
qtdemux->n_sub_streams = 0;
qtdemux->exposed = FALSE;
qtdemux->fragmented = FALSE;
qtdemux->mss_mode = FALSE;
qtdemux->variant = VARIANT_NONE;
gst_caps_replace (&qtdemux->media_caps, NULL);
qtdemux->timescale = 0;
qtdemux->got_moov = FALSE;
@ -2072,7 +2074,7 @@ gst_qtdemux_reset (GstQTDemux * qtdemux, gboolean hard)
g_free (qtdemux->preferred_protection_system_id);
qtdemux->preferred_protection_system_id = NULL;
}
} else if (qtdemux->mss_mode) {
} else if (qtdemux->variant == VARIANT_MSS_FRAGMENTED) {
gst_flow_combiner_reset (qtdemux->flowcombiner);
g_ptr_array_foreach (qtdemux->active_streams,
(GFunc) gst_qtdemux_stream_clear, NULL);
@ -3528,7 +3530,7 @@ qtdemux_find_stream (GstQTDemux * qtdemux, guint32 id)
if (stream->track_id == id)
return stream;
}
if (qtdemux->mss_mode) {
if (qtdemux->variant == VARIANT_MSS_FRAGMENTED) {
/* mss should have only 1 stream anyway */
return QTDEMUX_NTH_STREAM (qtdemux, 0);
}
@ -3595,7 +3597,7 @@ qtdemux_parse_tfhd (GstQTDemux * qtdemux, GstByteReader * tfhd,
(*stream)->stsd_sample_description_id = sample_description_index - 1;
}
if (qtdemux->mss_mode) {
if (qtdemux->variant == VARIANT_MSS_FRAGMENTED) {
/* mss has no stsd entry */
(*stream)->stsd_sample_description_id = 0;
}
@ -4194,7 +4196,9 @@ qtdemux_parse_moof (GstQTDemux * qtdemux, const guint8 * buffer, guint length,
pssh_node = qtdemux_tree_get_sibling_by_type (pssh_node, FOURCC_pssh);
}
if (!qtdemux->upstream_format_is_time && !qtdemux->first_moof_already_parsed
if (!qtdemux->upstream_format_is_time
&& qtdemux->variant != VARIANT_MSE_BYTESTREAM
&& !qtdemux->first_moof_already_parsed
&& !qtdemux->received_seek && GST_CLOCK_TIME_IS_VALID (min_dts)
&& min_dts != 0) {
/* Unless the user has explicitly requested another seek, perform an
@ -7372,7 +7376,7 @@ gst_qtdemux_process_adapter (GstQTDemux * demux, gboolean force)
}
/* in MSS we need to expose the pads after the first moof as we won't get a moov */
if (demux->mss_mode && !demux->exposed) {
if (demux->variant == VARIANT_MSS_FRAGMENTED && !demux->exposed) {
QTDEMUX_EXPOSE_LOCK (demux);
qtdemux_expose_streams (demux);
QTDEMUX_EXPOSE_UNLOCK (demux);

18
subprojects/gst-plugins-good/gst/isomp4/qtdemux.h
View file

@ -65,6 +65,19 @@ enum QtDemuxState
QTDEMUX_STATE_BUFFER_MDAT /* Buffering the mdat atom */
};
typedef enum {
/* Regular behaviour */
VARIANT_NONE,
/* We're working with a MediaSource Extensions ISO BMFF Bytestream. */
VARIANT_MSE_BYTESTREAM,
/* We're working with a smoothstreaming fragment.
* Mss doesn't have 'moov' or any information about the streams format,
* requiring qtdemux to expose and create the streams */
VARIANT_MSS_FRAGMENTED,
} Variant;
struct _GstQTDemux {
GstElement element;
@ -137,10 +150,7 @@ struct _GstQTDemux {
guint32 segment_seqnum;
/* flag to indicate that we're working with a smoothstreaming fragment
* Mss doesn't have 'moov' or any information about the streams format,
* requiring qtdemux to expose and create the streams */
gboolean mss_mode;
Variant variant;
/* Set to TRUE if the incoming stream is either a MSS stream or
* a Fragmented MP4 (containing the [mvex] atom in the header) */