[FFmpeg-user] Building framemd5 checksum for Audio per second

[Kieran O Leary]

Hi,

On Wed, Jul 24, 2019 at 9:46 AM Bauer, Christoph <
Christoph.Bauer at slub-dresden.de> wrote:

> Hello everybody,
>
> I was building framemd5-checksums for Audio with 96kHz sampling for every
> second, using this command line:
>
> ffmpeg -i INPUT.mka -filter_complex "asetnsamples=n=96000" -f framemd5
> OUTPUT.framemd5
>
> The framemd5-file I get out of this starts with these lines:
>
> #format: frame checksums
> #version: 2
> #hash: MD5
> #software: Lavf58.27.102
> #tb 0: 1/96000
> #media_type 0: audio
> #codec_id 0: pcm_s16le
> #sample_rate 0: 96000
> #channel_layout 0: 3
> #channel_layout_name 0: stereo
> #stream#, dts,        pts, duration,     size, hash
> 0,          0,          0,    96000,   384000,
> 1fd71ae8708c0b45e229b1d823eb362b
> 0,      96000,      96000,    96000,   384000,
> 2b9a626285c754e3b39d1555f202ad81
> 0,     192000,     192000,    96000,   384000,
> 8e9a791e7d5126e5208416f412f3ab26
>
> The same file was delivered with a framemd5-file which starts with those
> lines:
>
> #format: frame checksums
> #version: 2
> #hash: MD5
> #software: Lavf58.20.100
> #tb 0: 1/96000
> #media_type 0: audio
> #codec_id 0: pcm_s24le
> #sample_rate 0: 96000
> #channel_layout 0: 3
> #channel_layout_name 0: stereo
> #stream#, dts,        pts, duration,     size, hash
> 0,          0,          0,    96000,   576000,
> 2b31df8f73cf3d95b236d2dd16e6ba30
> 0,      96000,      96000,    96000,   576000,
> ebb8f1f3efde3fda9cb21ecd959ea076
> 0,     192000,     192000,    96000,   576000,
> 1a01031d660895b43f92234f2582a6a8
>
> The difference between the checksum-files is as far that i can see at
> first the software (Lavf58.20.100 vs. Lavf58.27.102), at second the
> codec_id  (pcm_s24le vs. pcm_s16le) and thirdly  the size (576000 vs.
> 384000). Now my questions are the following:
>
> The version of lavf most likely isn't the issue, but the audio format
would be why there's different framemd5s and sizes.


>
> -          Is it possible to get out those different framemd5-files out
> of the same file?
>

Probably - ffmpeg defaults to decoding as 16-bit for framemd5 for audio. So
whoever made the 24-bit framemd5 probably added `-c:a pcm_s24le` to their
framemd5 command. You should add the same to your framemd5 command.
 I don't know if this will produce the same framemd5s or not, but I've had
to force pix_fmt sometimes in order to get matching image framemd5s.


>
> -          Which parameters have to be added or changed in the command
> line above to get the result oft he second framemd5-file?
>

by adding `-c:a pcm_s24le` this time?
ffmpeg -i INPUT.mka -filter_complex "asetnsamples=n=96000" -c:a pcm_s24le
-f framemd5 OUTPUT.framemd5

This is just what I'd try, curious to know if it would work.

Best,

Kieran O'Leary
Irish Film Institute.

>
>
> Thanks in advance
>
> Christoph
>
>
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