Playbin2 with file whose length changes

[Jeffrey Barish]

Does anyone know what happens with playbin2 when the length of the file
increases after initiating play?  Does playbin2 read the duration of the
file either when it updates the uri property or when it goes into play mode?
--
Jeffrey Barish


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[Stefan Sauer]

Jeffrey Barish wrote:
> Does anyone know what happens with playbin2 when the length of the file
> increases after initiating play?  Does playbin2 read the duration of the
> file either when it updates the uri property or when it goes into play mode?
>  
playbin2 itself does not care about the length. The length can also
change in the case of vbr when betetr stimates are available.

Stefan

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[Philippe Normand]

You can listen for GST_MESSAGE_DURATION messages on the bus to get
notified of duration changes.

My 2 cents :)
Philippe

On Tue, 2010-01-19 at 17:37 +0200, Stefan Kost wrote:

> Jeffrey Barish wrote:
> > Does anyone know what happens with playbin2 when the length of the file
> > increases after initiating play?  Does playbin2 read the duration of the
> > file either when it updates the uri property or when it goes into play mode?
> >  
> playbin2 itself does not care about the length. The length can also
> change in the case of vbr when betetr stimates are available.
>
> Stefan
>
> ------------------------------------------------------------------------------
> Throughout its 18-year history, RSA Conference consistently attracts the
> world's best and brightest in the field, creating opportunities for Conference
> attendees to learn about information security's most important issues through
> interactions with peers, luminaries and emerging and established companies.
> http://p.sf.net/sfu/rsaconf-dev2dev
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[Jeffrey Barish]

Philippe Normand wrote:

> On Tue, 2010-01-19 at 17:37 +0200, Stefan Kost wrote:
>> Jeffrey Barish wrote:
>> > Does anyone know what happens with playbin2 when the length of the file
>> > increases after initiating play?  Does playbin2 read the duration of
>> > the file either when it updates the uri property or when it goes into
>> > play mode?
>> >  
>> playbin2 itself does not care about the length. The length can also
>> change in the case of vbr when betetr stimates are available.
>>
>> Stefan
>
> You can listen for GST_MESSAGE_DURATION messages on the bus to get
> notified of duration changes.
>
> My 2 cents :)
> Philippe

The GST_MESSAGE_DURATION message is interesting, although in my quick test I
don't seem to be getting it.  In any case, I don't really need to know that
the length changed, I just need for playbin2 to play the entire file.  Is
that what is meant by "does not care about the length"?

Here's what I observe, by way of example: Suppose that I start playing when
the sound file has a length of 1 sec.  A short time after starting play (and
well before play reaches the end of the sound file), the length of the sound
file grows to 10 seconds.  No matter.  Play stops at 1 second and there is
an EOS message on the bus.

There is nothing in my code that reads the length of the file, so I think
the problem has to be with GStreamer or with the way I am using it.
--
Jeffrey Barish


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[Tim-Philipp Müller-2]

On Tue, 2010-01-19 at 13:22 -0700, Jeffrey Barish wrote:

> The GST_MESSAGE_DURATION message is interesting, although in my quick test I
> don't seem to be getting it.  In any case, I don't really need to know that
> the length changed, I just need for playbin2 to play the entire file.  Is
> that what is meant by "does not care about the length"?

There's the length/duration in time, estimations of which may change
while playing back the file (e.g. in case of a VBR mp3 file) even if the
original file doesn't change, and then there's length in bytes of the
original input file. In the first case you should/might get a DURATION
message.


> Here's what I observe, by way of example: Suppose that I start playing when
> the sound file has a length of 1 sec.  A short time after starting play (and
> well before play reaches the end of the sound file), the length of the sound
> file grows to 10 seconds.  No matter.  Play stops at 1 second and there is
> an EOS message on the bus.
>
> There is nothing in my code that reads the length of the file, so I think
> the problem has to be with GStreamer or with the way I am using it.

Many GStreamer plugins current don't handle files expanding while
they're being read from very well. For many cases this may not be too
difficult to fix up though, but it will likely need to be fixed at the
parser/demuxer level, so depends a lot on the file type. A little test
program to test this kind of thing would be quite useful.

 Cheers
  -Tim



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