[gst-devel] Transcoding and otherwise dealing with streams.

[Baldur Gislason]

I went back to basics, building some test pipelines by hand with gst-launch.
Same result as before, if I create the pipeline with decodebin or
decodebin2, I get output but the performance is terrible, maxes one
core at 100% and real time transcoding becomes impossible.
If I construct a pipeline by hand using mpegtsdemux, mpeg2dec, x264enc
and mpegtsmux, transcoding video only works great, and performance is
as expected, using about 20% CPU time on this quad core Xeon E5507
machine. However when I try to pass audio through that pipeline, I get
a deadlock somewhere and nothing comes out of the TS mux.

Decodebin pipeline that works but performs very bad:
gst-launch-0.10 -v mpegtsmux name ="mux" ! filesink
location="/home/baldur/launch.ts" \
udpsrc multicast-group="239.192.192.1" port=1234 ! decodebin2 name="d"
{ d. ! queue ! x264enc key-int-max=50 ip-factor=0.71 analyse=0x113
me=0 subme=1 bframes=3 trellis=0 interlaced=1 ! queue
max-size-buffers=16384 ! mux. } \
{ d. ! audioconvert ! audioresample ! ffenc_aac ! queue
max-size-time=10000000000 ! mux. }

Discrete pipeline that works and performs great for video only:
gst-launch-0.10 -v mpegtsmux name ="mux" ! filesink
location="/home/baldur/launch.ts" \
udpsrc multicast-group="239.192.192.1" port=1234 ! mpegtsdemux
name="d" { d. ! queue ! mpeg2dec ! x264enc key-int-max=50
ip-factor=0.71 analyse=0x113 me=0 subme=1 bframes=3 trellis=0
interlaced=1 ! queue ! mux. }

Discrete pipeline that does not feed anything through it, CPU usage
goes up for a while, until it fills some queue I guess and then it
stops. Nothing is ever written to the filesink:
gst-launch-0.10 -v mpegtsmux name ="mux" ! filesink
location="/home/baldur/launch.ts" \
udpsrc multicast-group="239.192.192.1" port=1234 ! mpegtsdemux
name="d" { d. ! queue ! mpegvideoparse ! mpeg2dec ! x264enc
key-int-max=50 ip-factor=0.71 analyse=0x113 me=0 subme=1 bframes=3
trellis=0 interlaced=1 ! queue ! mux. } \
{ d.audio_%04x ! queue max-size-time=10000000000
max-size-buffers=16384 ! mp3parse ! mux. }

Another discrete that feeds nothing:
gst-launch-0.10 -v mpegtsmux name ="mux" ! filesink
location="/home/baldur/launch.ts" \
udpsrc multicast-group="239.192.192.1" port=1234 ! mpegtsdemux
name="d" { d. ! queue ! mpegvideoparse ! mpeg2dec ! x264enc
key-int-max=50 ip-factor=0.71 analyse=0x113 me=0 subme=
1 bframes=3 trellis=0 interlaced=1 ! queue ! mux. } \
{ d. ! queue ! ffdec_mp3 ! audioconvert ! audioresample ! ffenc_aac !
queue ! mux. }

I have tried a bunch of configurations on the audio side, but can't
seem to get any audio through.
Output from gst-launch for decodebin based pipeline:
http://pastebin.com/LRUnZhEf
I don't see anything in the output that I am missing from the other pipeline.

Baldur

On Sat, Sep 18, 2010 at 2:31 PM, Marco Ballesio <gibrovacco at gmail.com> wrote:
> Hi,
>
> sorry for the late reply. I hope it will help.
>
> On Fri, Sep 10, 2010 at 7:52 PM, Baldur Gislason <baldur at medizza.com> wrote:
>>
>> I am trying to construct a C application that can either pick up
>> audio/video from a file (mpeg transport stream) or receive mpeg  transport
>> stream on a UDP socket.
>> Input format is MPEG2 A/V and output is H.264 with MPEG audio or AAC,
>> transport stream multiplexing on output.
>> So far I have managed to transcode video from network but am getting
>> buffer underruns on the queue. If I add audio everything just stops, the
>> pipeline does nothing and I can't quite figure out why.
>
> I don't have many details about how your pipelines ar4e built, but in 90% of
> the cases the behaviour you're observing is due to a missing queue at the
> right point. The audio thread should be straightforward from source to sink,
> while one queue element should be separating the video thread before the
> muxer.
>
>>
>> If I read the data from a file, I get buffer overruns. So clearly this is
>> a clocking thing. I have searched for documentation regarding clocking in
>> gstreamer but found nothing useful.
>
> You can find something here:
>
> http://cgit.freedesktop.org/gstreamer/gstreamer/tree/docs/design/part-clocks.txt
>
> and here:
>
> http://cgit.freedesktop.org/gstreamer/gstreamer/tree/docs/design/part-scheduling.txt
> http://cgit.freedesktop.org/gstreamer/gstreamer/tree/docs/design/part-synchronisation.txt
>
>>
>> The app developers manual mentions clocking but nothing about how it
>> applies to code, and gst-inspect says none of the elements I have looked at
>> have any clocking capabilities?!f
>>
>> Anyway, I was wondering if anyone had an example for building an MPEG
>> transcoding pipeline in C, for working with a live stream and not file
>> input, file output. File input, network output would be the other
>> scenario.
>
> See here the excellent guide (should be from Mark Nauwelaerts):
>
> http://gentrans.sourceforge.net/docs/head/manual/html/howto.html
>
> Regards
>
>>
>> Baldur Gislason
>>
>>
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