gapless playback

[stuart68]

Hi,

I am seeking some guidance with respect to getting gapless playback using decodebin2 and queue2.

Our system comprises the following:

arm9 processor
gst-plugins-bad - 0.10.20-r11.0.6
gst-plugins-base - 0.10.31-r11.0.6
gst-plugins-good - 0.10.25-r11.0.6
gst-plugins-ugly - 0.10.16-r11.1.6
running on openembedded linux with kernel version 2.6.33

We are decoding audio only streams. This is a concern as reference was made to gapless playback for the latest releases:

"Release notes for GStreamer Base Plug-ins?0.10.31 "Dance Like It's 1982"

Bugs fixed in this release

     * 628028 : [uridecodebin] Don't enable progressive downloading for live streams
     * 623846 : typefinding: add support for " enhanced ac3 " (eac3)
     * 602437 : [playbin2] [gapless] Completely broken when switching between files with audio/video only
"

The above refers directly to playbin2, but is there anything related when using decodebin2 and queue2 as I would assume playbin2 would use these also.

At present we have definite breaks with clicks between tracks.

Any help is greatly appreciated....

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[Marco Ballesio]

Hi,

On Thu, Dec 16, 2010 at 3:58 AM, Stuart Gray <[hidden email]> wrote:

> Hi,
>
> I am seeking some guidance with respect to getting gapless playback using
> decodebin2 and queue2.
>
> Our system comprises the following:
>
> arm9 processor
> gst-plugins-bad - 0.10.20-r11.0.6
> gst-plugins-base - 0.10.31-r11.0.6
> gst-plugins-good - 0.10.25-r11.0.6
> gst-plugins-ugly - 0.10.16-r11.1.6
> running on openembedded linux with kernel version 2.6.33
>
> We are decoding audio only streams. This is a concern as reference was made
> to gapless playback for the latest releases:
>
> "Release notes for GStreamer Base Plug-ins?0.10.31 "Dance Like It's 1982"
>
> Bugs fixed in this release
>
>      * 628028 : [uridecodebin] Don't enable progressive downloading for live
> streams
>      * 623846 : typefinding: add support for " enhanced ac3 " (eac3)
>      * 602437 : [playbin2] [gapless] Completely broken when switching
> between files with audio/video only
> "
>
> The above refers directly to playbin2, but is there anything related when
> using decodebin2 and queue2 as I would assume playbin2 would use these also.
>
> At present we have definite breaks with clicks between tracks.
>
> Any help is greatly appreciated....

afaiu the gapless playback concept in playbin2 is based on the
"about-to-finish" signal:

http://www.gstreamer.net/data/doc/gstreamer/head/gst-plugins-base-plugins/html/gst-plugins-base-plugins-playbin2.html#GstPlayBin2-about-to-finish

which appears to be playbin2 specific, but let's not give up with hopes now.

As the signal is emitted from the handler of the "drained" signal, in
turn emitted from uridecodebin/decodebin2, you can use it to prepare
the next track in your app. Still you'll have to implement by yourself
the handling logic as in the following functions (I'm sorry not to put
a link to the gitweb source but freedesktop is awfully unstable
today):

- drained_cb: the handler of the "drained" signal.
- activate_group: (the most noteworthy) re-sets the pipeline and puts
in it in the appropriate state.

Essentially, you'll need to set all the pipeline properties in the
signal handler, as implemented in activate_group.

These (intermediate) functions may be interesting to understand how
playbin2 internally handles the transition:

- gst_play_bin_set_suburi: to store the next URI to be played.
- setup_next_source: called by the drained_cb callback after the new
URI has been set with gst_play_bin_set_uri. It essentially prepares
the playbin2 internals for the next uri.

all the functions are in [gst-plugins-good]/gst/playback/gstplaybin2.c

This is not much, but hopefully it's at least a good starting point..

Regards

>
> ------------------------------------------------------------------------------
> Lotusphere 2011
> Register now for Lotusphere 2011 and learn how
> to connect the dots, take your collaborative environment
> to the next level, and enter the era of Social Business.
> http://p.sf.net/sfu/lotusphere-d2d
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>
>

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[Sebastian Dröge-7]

On Thu, 2010-12-16 at 09:58 +0800, Stuart Gray wrote:

> Hi,
>
> I am seeking some guidance with respect to getting gapless playback
> using decodebin2 and queue2.
>
> Our system comprises the following:
>
> arm9 processor
> gst-plugins-bad - 0.10.20-r11.0.6
> gst-plugins-base - 0.10.31-r11.0.6
> gst-plugins-good - 0.10.25-r11.0.6
> gst-plugins-ugly - 0.10.16-r11.1.6
> running on openembedded linux with kernel version 2.6.33
>
> We are decoding audio only streams. This is a concern as reference was
> made to gapless playback for the latest releases:
>
> "Release notes for GStreamer Base Plug-ins?0.10.31 "Dance Like It's
> 1982"
>
> Bugs fixed in this release
>
>      * 628028 : [uridecodebin] Don't enable progressive downloading
> for live streams
>      * 623846 : typefinding: add support for " enhanced ac3 " (eac3)
>      * 602437 : [playbin2] [gapless] Completely broken when switching
> between files with audio/video only
> "
>
> The above refers directly to playbin2, but is there anything related
> when using decodebin2 and queue2 as I would assume playbin2 would use
> these also.
>
> At present we have definite breaks with clicks between tracks.

The gapless playback is handled inside playbin2/playsink only. You can't
do it with only decodebin2 unless you're building the same logic around
it.

Note however, that short before 0.10.31 release the main fix for bug
#602437 was disabled again because it caused problems in other, standard
scenarios that worked before. As such gapless playback is still broken
in almost all cases (unless you're playing audio-only streams only).


As you're decoding audio-only streams you might want to take a look at
rhythmbox's gapless playback too. For audio-only streams there's a much
easier solution for gapless playback: you would simply write an element
that converts the different audio streams that it gets into one,
continous stream and then passes it to the sink. Just make sure that you
*never* change the sinks (changing the complete pipeline state will do
that) state to something below PLAYING, otherwise you'll hear gaps
again.

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