AV Content Integrity

What is that? Where's the difference to file MD5s?

Different level

• Content = The actual information stored as payload.
  
• Hashcode is taken from a normalized form of uncompressed.
  
• Matching "pix_fmt".

Scope

• Video: Each frame = 1 object
• Audio: Group of samples = 1 object

Use cases

• Format normalization
• Rewrap container
• Transcode
• Add/edit embedded metadata?

Which target formats support this?

The Tool

• ffmpeg

Algorithms

• frameCRC
• frameMD5

Hashing video

$ ffmpeg -i VIDEOFILE
 -an 
 -f framemd5 
 VIDEOFILE.framemd5

Hashing audio

$ ffmpeg -i VIDEOFILE 
 -vn 
 -filter_complex "asetnsamples=n=96000"
 -f framemd5
 VIDEOFILE.audio.framemd5

Which samplerate to choose here?

Modify the content

Rewrap container

...and add/edit metadata!

$ ffmpeg -i VIDEO_IN
 -c copy 
 -map 0 
 VIDEO_OUT.mkv

-map 0: "re-encode just the video streams, but copy all the other streams (like audio, subtitles, attachments, etc)"

Transcode to FFV1

$ ffmpeg -i VIDEO_IN
 -c:a copy
 -c:v ffv1
 -g 1
 -pix_fmt +
 VIDEO_OUT.mkv

-pix_fmt +: Preserve or die.

Validating framemd5

Framemd5 is actually just a plain textfile...

Using a diff tool

"Meld is a visual diff and merge tool targeted at developers."

Diff is just one (nice) option: Website: meldmerge.org

Comparing framemd5s

Hashes match, but other (irrelevant) text doesn't:

Adjusting diff filters

Comparing framemd5s

Exercise

Let's go back and actually do all that! :D

RAWcooked

"It's like 'zip-for-film™', and super-easy to use!"

Quote Source

Features

• DPX to FFV1
• WAV to FLAC
• Multi reels = multiple tracks
• Other files: embed as-is
• 100% reversible.

Website: mediaarea.net/RAWcooked

Exercise

• Create bag for DPX/WAV sequence
• Convert bag to RAWcooked FFV1/FLAC/MKV
• Uncompress back to DPX.
• Validate bag.

Links

• Video per-frame integrity check - verifying losslessness

Questions?

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