demuxing mp4 and queues

[David Ing]

I have also learned that queues are needed on the branches of a tee (for
probably the same reasons).

For more information on what I learned about queues and tees:
http://gstreamer-devel.966125.n4.nabble.com/Usage-of-tee-with-queue-td4689894.html

There is also some great documentation about how queues function as thread
boundaries:
https://gstreamer.freedesktop.org/documentation/application-development/advanced/threads.html

On Wed, Mar 6, 2019 at 3:45 AM Mathieu Duponchelle <mathieu at centricular.com>
wrote:

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