[gst-devel] Selective decoding of video packets

[Timothy Braun]

I'm not guru with GST by any means.  But some things you may want to look
into below:

On Sun, Dec 19, 2010 at 10:51 AM, Rohit Atri <rohitratri at gmail.com> wrote:

> Come on, guys! Someone's got to know where I'm stuck.
> All you GST gurus out there, please help me out.
>
> Thanks
>
> On Sat, Dec 18, 2010 at 9:12 PM, Rohit Atri <rohitratri at gmail.com> wrote:
>
>> Hi,
>>
>> I m writing an application which reads mp4 packets from a file (bin1:
>> filesrc->qtdemux->appsink), do some analysis on a set(say 100 - depending on
>> the duration of the video) of packets and choose one single packet and send
>> it for decoding (bin2: appsrc->ffdec_mpeg4->appsink) and then save this
>> image... repeat the process for all packets in the video.
>> I've a few questions -
>> 1. Are the elements I'm using apt?  and do I've to do some thread
>> management since I've to pipelines?
>>
>
GST does quite a bit of thread management on it's own.  It builds the logic
into the pipeline using various layers of queues and multiqueues.


> 2. a. I'm able to receive packets from bin1, do some analysis and send a
>> single packet(iFrame) for decoding.. but bin2 doesn't return the packet
>> back(the application hangs!)..
>>
>
Is it possible that the single packet isn't enough to fulfill the segment?
Take a look at the debug output of ffdec, is it spitting off buffer
underflow warnings?


> b. When I turn on the logs with level-4, I do get the packet back!!! - so
>> it could be timing issue, I suspect.
>>
>
Not sure where this is coming from, but you may want to throw a queue
between your appsrc and ffdec so it would be appsrc->queue->ffdec


> c. The bin1 returns say 200 or so packets and the app receives an EOS
>> message from it! - why is that?
>>
>
Not sure where the EOS is coming from, but you may want to look into
blocking pads to control pipeline flow.  Also take a look at the 'eos'
property on the appsink element, this may be what's causing your issue, but
I'm just guessing here.


> 3. Does appsink return packets as and when it receives them or does it wait
>> to preroll?
>>
>>
No idea here, sorry.


> Please help me understand the situation better. I've hit a roadblock!
>> Please let me know if you need some logs...
>>
>> Thanks
>> Rohit
>>
>
>
>
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