[mythtv] Corrupted ac3 audio handling in 0.22
digitalaudiorock at gmail.com
Thu Feb 25 21:53:18 UTC 2010
On Thu, Feb 25, 2010 at 3:58 PM, Tom Dexter <digitalaudiorock at gmail.com> wrote:
> Back in 0.21 I submitted an ffmpeg patch that prevented loud audio
> chirps in corrupted ac3 audio:
> That essentially replaced the loud chirps with silence (complete
> dropout of the audio).
> It appears that since then, ffmpeg now has the some sort of error
> concealment (as was noted in the TODO comment on the original fix). I
> believe this is controlled via this bitmask in
> enc->error_concealment = FF_EC_GUESS_MVS | FF_EC_DEBLOCK;
> ...as per this (in libs/libavcodec/avcodec.h):
> * error concealment flags
> * - encoding: unused
> * - decoding: Set by user.
> int error_concealment;
> #define FF_EC_GUESS_MVS 1
> #define FF_EC_DEBLOCK 2
> ...though I don't know anything about either one.
> I've noticed that since upgrading, when I have any bad ac3 (from bad
> weather reception for example), rather than getting silence I get a
> real annoying mid-range tone. While it's much better than the full
> scale chirps that would about knock you off your seat, it's _way_ more
> annoying than dropouts.
> Has anyone else noticed this, or is anyone clear on those flags? Thanks.
It appears (I believe) that that bitmask only affects video handling.
It appears that now, when the ac3 has a crc mismatch, they end up
setting the audio channels in a different manner, but continuing with
the decode of the audio rather than dropping the frame.
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