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

[Bouke / edit 'B]

On 3 Aug 2023, at 11:12, Bouke / edit 'B <bouke at editb.nl> wrote:
> 
> 
>> 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.

Nah, I just ran a check, FFmpeg IS using ONLY the Data chunk for MD5
(Minus the ‘Data’ and chunk size)

So it ’should’ work straight out of the box.

Bouke


> Bouke
> 
>> 
>> 
>> --
>> 
>> Thanks,
>> 
>>       Stuart Robinson,
>> 
>>       AV Technician,
>> 
>>       Sound Lab,
>> 
>>       School of Scottish Studies,
>> 
>>       University of Edinburgh,
>> 
>>       29 George Square,
>> 
>>       Edinburgh,
>> 
>>       EH8 9LD
>> 
>> 
>> 
>>       0131 651 5001
>> 
>> 
>> 
>> 
>> 
>> The University of Edinburgh is a charitable body, registered in
>> 
>> Scotland, with registration number SC005336.
>> 
>> 
>> ________________________________
>> 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
>> 
>> This email was sent to you by someone outside the University.
>> You should only click on links or attachments if you are certain that the email is genuine and the content is safe.
>> 
>>> 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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