[FFmpeg-devel] [PATCHv2] af_hdcd: Don't warn if converting from AV_SAMPLE_FMT_S16P

[Burt P.]

Are you now talking about plans of the future or this specific case?

As it is, automatic conversion is very helpful, for example from
WavePack, which uses s16p.
This filter is only looking at the AVFilterLinks between filters, not
at the filters themselves.
This scan and warn behavior was added to address a real issue.

Consider these example cases:
ffmpeg -i hdcd16.wv -af hdcd hdcd24.flac
* .wv uses s16p, auto-converted to s16, nice!
* hdcd is decoded without problem
* 24-bit flac is output, ok

ffmpeg -i hdcd16.wv -af hdcd hdcd24-expected.wav
* .wv uses s16p, auto-converted to s16, nice!
* hdcd is decoded without problem
* s32 is converted to s16 for wav by default, but user expects it to
be more than 16-bit!
--- a warning is issued about the truncation

ffmpeg -i hdcd16.flac -af hdcd hdcdout.m4a
* .flac has s16 samples, passed without problem
* hdcd is decoded without problem
* native aac encodes the full range, ok!

ffmpeg -i hdcd16.flac -af hdcd -c:a libfdk_aac hdcd-dec.m4a
* .flac has s16 samples, passed without problem
* hdcd is decoded without problem
* autoconverted to s16 for libfdk-aac, but the user doesn't know that
the "best available aac encoder" only accepts s16 input!
--- a warning is issued about the truncation

ffmpeg -i anything_not_s16 -af hdcd hdcd24.flac
* input is anything that is not likely to have hdcd
* it is converted to s16 for the filter
--- a warning is issued about the format conversion

I think the automatic conversion from s16p, and into fltp when needed
is very good and I'd like to keep it, but I would also like to warn
when there might be a problem.
As I understand it though, you think auto-inserted filters should be
off, and the user will have to manually add conversions for
WavePack/s16 and the like before, and conversion to fltp, s24, etc.
after.


On Sun, Aug 7, 2016 at 5:23 PM, Nicolas George <george at nsup.org> wrote:
> Le primidi 21 thermidor, an CCXXIV, Carl Eugen Hoyos a écrit :
>> Wouldn't that disable any automatic conversion behind (after) the
>> hdcd filter? If that is correct, I would not consider it a better solution.
>
> The filter already checks for conversions after itself too.
>
> Conversion can still happen, but only at explicit points.
>
> Regards,
>
> --
>   Nicolas George
>
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-- 
Burt