[gst-devel] appsrc vs filesrc problem

Richard123 buteo.rg at googlemail.com
Wed Jul 7 10:59:18 CEST 2010




On Tue, Jul 6, 2010 at 12:01 PM, Richard123 <buteo.rg at googlemail.com> wrote:

>
> Hi,
>
> Using an identity element, I have compared buffer data file dumps of both
> appsrc and filesrc elements.
> (filesrc, - appears to have repeated several pre-roll GstBuffers).
>
> Can anyone explain why appsrc (only works if I use very large buffer
> sizes),
> or perhaps provide suggestions on why filesrc repeats buffers?
>

It's hard to know unless you give us more context, you could start by
telling us what pipelines are you using or any other information you might
find relevant.


>
> Many thanks,
> Richard
>
Hi,

Thanks for your reply.

I am trying to write an application which decodes live TS data using a
capture card, (appsrc to push buffers into my pipeline). I noticed a
correlation between buffer size and decode errors; (using default 4096 bytes
produces huge amounts of errors)

In an effort to understand the difference between filesrc and appsrc, I have
written two small similar programs, to compare buffer dumps. The pipeline I
am using is as follows:

Prog 1) filesink ! identity ! decodebin2 ! xvimagesink (produces no decode
errors)
Prog 2) appsrc ! identity ! decodebin2 ! xvimagesink (produces decode errors
depending on buffer size)

I then connect to the handoff signal to dump GstBuffers, (out of identity
element) to a file. 

Comparing buffer dumps, I noticed the following:
1) During the pre-roll phase, filesrc sends the same buffers more than once;
(approx sixty buffers)
2) Again during pre-roll, filesrc buffer sizes changed; ie. buff1=4096
bytes, buff2=32bytes, buff3=128bytes, buff4=4096 bytes.
3) After the pre-roll phase both files are identical

So my question is; how can I pre-roll the pipeline in a manner consistent
with filesrc?

Kind regards,

Richard

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