[FFmpeg-user] ac3 frame sync errors mpegts->webm chunks

Moritz Barsnick barsnick at gmx.net
Wed Aug 3 20:39:19 EEST 2016

On Wed, Aug 03, 2016 at 10:15:09 -0500, Sam Gardner wrote:
> I've attacted a file that exhibits all behavior - as you can see from the
> earlier logs, an identically-compiled/configured ffmpeg 2.8.7 has the same
> behavior on the same input.

I don't understand which error you are describing. ffmpeg (HEAD) with
your sample shows similar errors as your original email, but decoding
works up to that error. And when it occurs, I think the sample is over
(approx. 30 seconds).

Your sample "sort of" works for me, but it is the most broken transport
stream I have seen in a while, typical from a bad tuner (or bad
weather). Both the video and the audio stream throw *tons* of errors
before they terminate, but your logs don't show there.

> bin/hdhomerun_config 10391104 save /tuner0 - | /home/sam/bin/ffmpeg -i - *-map
> i:0x31 *-pix_fmt yuv420p -c:v libvpx-vp9 -s 640x360 -keyint_min 60 -g 60
> -speed 6 -tile-columns 4 -frame-parallel 1 -threads 8 -static-thresh 0
> -max-intra-rate 300 -deadline realtime -lag-in-frames 0 -error-resilient 1 -b:v 1000k -f webm_chunk -header
> /var/www/html/webm_live/tuner_720.hdr -chunk_start_index 1
> /var/www/html/webm_live/tuner_720_%d.chk *-map i:0x35* -c:a libvorbis -b:a
> 128k -af 'pan=stereo|c0=FL|c1=FR' -f webm_chunk -audio_chunk_duration 2000
> -header /var/www/html/webm_live/tuner_128.hdr -chunk_start_index 1
> /var/www/html/webm_live/tuner_128_%d.chk

I can only use your sample, and it shows a different output. This makes
trying to understand your issue quite difficult. Can you provide a
sample which exactly exposes the error you're trying to point out=

As Carl Eugen mentioned, it is most likely a decoder error. So I would
use a command line which basically only decodes, like
$ ffmpeg -i capture.ts -map 0:1 -f null -
$ ffmpeg -i capture.ts -map 0:2 -f null -
and try to see whether that exposes unexpected behavior.

> *Successful Output (just trust me that it's working okay - the input is in
> bad shape but I can't figure out how to capture the logs in a way that's
> gmail-readable)*

You could add "-report" and attach the report file.

> Stream mapping:
>   Stream #0:0 -> #0:0 (mpeg2video (native) -> vp9 (libvpx-vp9))
>   Stream #0:2 -> #1:0 (ac3 (native) -> vorbis (libvorbis))
> ...

But this is success, right? What's the issue here?

> > Stream mapping:
> >   Stream #0:0 -> #0:0 (mpeg2video (native) -> vp9 (libvpx-vp9))
> >   Stream #0:1 -> #1:0 (ac3 (native) -> vorbis (libvorbis))
> > [ac3 @ 0x2ed6060] frame sync error
> > Error while decoding stream #0:1: Invalid data found when processing input

And with my ffmpeg and your sample, I do get this, but apparently at
the *end* of the sample.


More information about the ffmpeg-user mailing list