[FFmpeg-user] Reading bwf metaedit md5 value with ffprobe

[Bouke / edit 'B]

> On 3 Aug 2023, at 10:49, Stuart Robinson <Stuart.Robinson at ed.ac.uk> wrote:
> 
>>> But then you have to store the checksum output somewhere, either in a sidecar file or a database. My recommendation would be to do it like this and store the checksum of the whole file. That way it will work with any kind of file in your processing chain - AVI, PDF, WAV, Matroska, etc
> 
>> My question, how is an application capable of storing a checksum inside a file it’s describing? Adding it will change the checksum…
> 
> Bouke
> _________________________________________________________________________________________________________________________________
> It only checksums the audio data. From the manual:
> 
> While the metadata is expected to change, the audio data is not. For this reason BWF MetaEdit supports the generation of an audio-data-only checksum (including the entire <data> chunk, excluding the chunk id, size declaration, and any optional padding byte). This will create a hash value for only the audio portion of the file which helps validate the integrity of the audio but allows for alteration of the metadata.
> 
> Wavelab uses the same method as the MD5s match.
> 
> I have been using this method of ensuring audio data integrity for a while and I was hoping to get a workflow using ffmpeg to verify and write them as well.

In that case, why not make raw audio with FFmpeg, and feed that to the checksum routine?
Should do the trick.

Bouke

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>        Stuart Robinson,
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> ________________________________
> From: ffmpeg-user <ffmpeg-user-bounces at ffmpeg.org> on behalf of Bouke / Videotoolshed <bouke at videotoolshed.com>
> Sent: 03 August 2023 08:51
> To: FFmpeg user questions <ffmpeg-user at ffmpeg.org>
> Subject: Re: [FFmpeg-user] Reading bwf metaedit md5 value with ffprobe
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>> On 3 Aug 2023, at 09:20, Tobias Rapp <t.rapp at noa-archive.com> wrote:
>> 
>> On 02/08/2023 17:43, Stuart Robinson wrote:
>>> I think Wavelab (since at least 8.5 and up to the current version) can also read and write that chunk so it must be standardised in some way.
>>> 
>>> I t would be useful to be able to do be able to read and write this tag, is it possible to make a feature request?
>>> 
>>> It seems to just tack on some data to the end of the file.
>>> 
>>> <?xpacket end="w"?>MD5    ÇúR
§üªû õ
°
%vþ
>>> 
>>> Thanks, Stuart
>>> 
>> From what I understand you could achieve the same effect (MD5 checksum of the data part only) using a command-line like:
>> 
>> ffmpeg -i INPUT.wav -f md5 -c copy - 2>NUL
>> 
>> But then you have to store the checksum output somewhere, either in a sidecar file or a database. My recommendation would be to do it like this and store the checksum of the whole file. That way it will work with any kind of file in your processing chain - AVI, PDF, WAV, Matroska, etc
> 
> My question, how is an application capable of storing a checksum inside a file it’s describing? Adding it will change the checksum…
> 
> Bouke
> 
> 
> 
>> Regards, Tobias
>> 
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