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This is a classical problem, and a good illustration why you usually
need queues after elements<br>
with N src pads, and before elements with N sink pads:<br>
<br>
The demuxer is pushing to its source pads from the same thread, and
if you have connected<br>
these source pads with sync=true sinks, their chain function blocks
until prerolling is done,<br>
that is until each sink with sync=true has received a buffer. Adding
queues decouples branches of<br>
the pipeline, as they will start their own streaming thread.<br>
<br>
<div class="moz-cite-prefix">On 3/5/19 11:11 PM, Wudo Balmus wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAJsrfX_H-5NKM65BO3M+K+-nDBHF5QGOeXnKVxad_FQ-fNgW_w@mail.gmail.com">
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<div>Hello,</div>
<div>I'm trying to demux and playback an mp4 file with
h.264 video and aac audio. This pipeline works fine:</div>
<div><br>
</div>
<div>gst-launch-1.0 -v filesrc location=working.mp4 !
qtdemux name=a a. ! queue ! avdec_h264 ! videoconvert !
autovideosink a. ! queue ! avdec_aac ! autoaudiosink</div>
<div><br>
</div>
<div>However when the queues are removed, it hangs,
nothing is played back:</div>
<div><br>
</div>
<div>gst-launch-1.0 -v filesrc location=working.mp4 !
qtdemux name=a a. ! avdec_h264 ! videoconvert !
autovideosink a. ! avdec_aac ! autoaudiosink</div>
<div><br>
</div>
<div>It works fine without a queue when I just try to
playback video without audio:</div>
<div><br>
</div>
<div>gst-launch-1.0 -v filesrc location=working.mp4 !
qtdemux name=a a. ! avdec_h264 ! videoconvert !
autovideosink</div>
<div><br>
</div>
<div>I'm trying to understand why queues are necessary in
this scenario. Cannot qtdemux just write data to
video/audio decoder without the queues?<br>
</div>
<div><br>
</div>
<div>Best regards,</div>
<div>Wudo<br>
</div>
</div>
</div>
</div>
</div>
<br>
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