[vlc-devel] Re: Do we have a MPEG expert in VLC?

[Gildas Bazin]

On Monday 08 December 2003 07:20, R. Bernstein wrote:
> Recently, I've been making steps to add SVCD subtitles to VLC.
> However even before this, I noticed that when subtitles are in the
> MPEG stream VLC seems to have problems. 
> 
> Here is the VCD with SVCD subtitles I'm using: 
>   http://www.vcdimager.org/pub/vcdimager/.testing/svcd_ogt_test_ntsc.zip
> 
> But I bet if you have your own favorite, that would cause the below
> problems too. I noticed it also with a MPEG that had CVD subtitles
> encoded as well. 
> 
> The errors before the dropout I get are 
> [00000181] main audio output warning: PTS is out of range (924916), 
dropping buffer
> [00000181] main audio output warning: PTS is out of range (898872), 
dropping buffer
> ... [31 or so more of these lines with decreasing PTS numbers]
> 
> er
> [00000181] main audio output warning: PTS is out of range (6778), dropping 
buffer
> [00000181] main audio output warning: PTS is out of range (-19322), 
dropping buffer
> [00000180] main video output warning: late picture skipped (177910)
> [00000180] main video output warning: late picture skipped (127998)
> [00000180] main video output warning: late picture skipped (94647)
> [00000180] main video output warning: late picture skipped (44617)
> [00000180] main video output warning: late picture skipped (32074)
> [00000179] main decoder debug: thread 131081: secret message triggered at 
src/misc/block.c:410 (Connection timed out)
> [00000173] mpeg_system input warning: mux_rate changed, expect cosmetic 
errors
> [00000173] mpeg_system input warning: mux_rate changed, expect cosmetic 
errors
> 

I just tried the above sample and the problem doesn't come from VLC but from 
the file itself. There are invalid SCR (system clock reference) timestamps 
happening randomly (?) in the stream. VLC relies on this information to 
read the stream at the right pace (contrary to other players like xine/
mplayer which don't use this info and synchronise everything on the audio 
output clock).

Here is an extract of the logs I produced:

[00000199] mpeg_system input warning: scr: 261600
[00000199] mpeg_system input warning: scr: 262200
[00000199] mpeg_system input warning: scr: 262800
[00000199] mpeg_system input warning: scr: 263400
[00000199] mpeg_system input warning: scr: 408856   <----- PROBLEM HERE
[00000207] alsa audio output warning: recovered from buffer underrun
[00000204] main decoder debug: thread 1155218384: secret message triggered 
at src/misc/block.c:410 (Connection timed out)
[00000203] main decoder debug: thread 1146829776: secret message triggered 
at src/misc/block.c:410 (Connection timed out)
[00000199] mpeg_system input warning: mux_rate changed, expect cosmetic 
errors
[00000199] mpeg_system input warning: scr: 264000
[00000199] mpeg_system input warning: mux_rate changed, expect cosmetic 
errors
[00000199] mpeg_system input warning: scr: 264600
[00000199] mpeg_system input warning: scr: 265200
[00000199] mpeg_system input warning: scr: 265800

> 
> And there are still the other open MPEG questions like 
> 
> how to get MPEG system to register the streams it is handling in the
> Stream/Media info.
> 

Well, the way ES are registered has changed recently and only a few demuxers 
(like mpeg ps/ts) still use the old way. Once they are converted to the new 
api (afaik, fenrir is working on this) this will be done automatically.

> Why multiple ES's with the same aspect ratio but different frame sizes
> are detected for those VCD MPEG such as here:
> http://www.vcdimager.org/pub/vcdimager/examples/test_svcd/
test_svcd_ntsc.xml
> 

Didn't have a look yet.

--
Gildas

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