[libav-tools] AC3 frame sync error

Philip Jägenstedt philip at foolip.org
Thu Oct 6 23:28:06 CEST 2011


On Thu, Oct 6, 2011 at 23:15, Philip Jägenstedt <philip at foolip.org> wrote:
> I'm attempting to use ffmpeg to encode archive-quality MPEG-2 for
> http://www.archive.org/details/jagenstedtska-slaktforeningen-visingso-1991-filmvisning
> and similar home videos.
>
> I've encoded using -target pal-dvd -b 8500k -aspect 4:3 -flags
> +ilme+ildct and the output MPEG-2 can be found at the above URL.
>
> When playing this or any similarly encoded file with MPlayer, I get
> these two messages:
>
> [ac3 @ 0x7f502a64b5e0]frame CRC mismatch
> [ac3 @ 0x7f502a64b5e0]frame sync error
>
> The frame sync error is also repeated on every seek. I've tried git
> versions of libav going back to v0.6, but it appears this is not a
> recent regression.
>
> Is this cause for concern? Is it the encoder or decoder that is buggy?
> Comparing the output of MPlayer's -dumpaudio of the original and
> encoded audio tracks the lengths are slightly different, with the
> encoded version being about 0.04 seconds delayed, but I'm not sure if
> that's related in any way.
>
> I want to do this right once, so any help is appreciated. Perhaps AC3
> is not even the best option for the purpose?

Sorry for the spam, some Googling turned up
https://lists.libav.org/pipermail/ffmpeg-user/2010-August/026430.html
on the same issue. With mplayer -demuxer lavf the problem goes away
and the -audiodump output is the same number of samples.

-- 
Philip Jägenstedt


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