24bit flac encoding

[Atrocia]

I have 48 KHz / 24 bit audio files created by the Zoom H1 audio recorder; e.g.:

$ mediainfo sample.WAV
General
Complete name : sample.WAV
Format : Wave
File size : 2.75 MiB
Duration : 10s 0ms
Overall bit rate : 2 304 Kbps

Audio
ID : 0
Format : PCM
Format settings, Endianness : Little
Codec ID : 1
Codec ID/Hint : Microsoft
Duration : 10s 0ms
Bit rate : 2 304 Kbps
Channel(s) : 2 channels
Sampling rate : 48.0 KHz
Bit depth : 24 bits
Stream size : 2.75 MiB (100%)

When I convert them to flac format, they become 16 bit:

$ ffmpeg -i sample.WAV sample.flac

...

$ mediainfo sample.flac
General
Complete name : sample.flac
Format : FLAC
Format/Info : Free Lossless Audio Codec
File size : 695 KiB
Duration : 10s 0ms
Overall bit rate : 569 Kbps
Writing application : Lavf53.0.3

Audio
Format : FLAC
Format/Info : Free Lossless Audio Codec
Duration : 10s 0ms
Bit rate mode : Variable
Bit rate : 563 Kbps
Channel(s) : 2 channels
Sampling rate : 48.0 KHz
Bit depth : 16 bits
Stream size : 687 KiB (99%)
Writing library : Lavf53.0.3

ffmpeg (git-N-29954-gfc19379) throws this warning - I don't know if it's relevant:

Incompatible sample format 's32' for codec 'flac', auto-selecting format 's16'

The 'flac' tool, from the flac project, handles these files correctly:

$ flac sample.WAV

...

$ mediainfo sample.flac
General
Complete name : sample.flac
Format : FLAC
Format/Info : Free Lossless Audio Codec
File size : 1.59 MiB
Duration : 10s 0ms
Overall bit rate : 1 336 Kbps

Audio
Format : FLAC
Format/Info : Free Lossless Audio Codec
Duration : 10s 0ms
Bit rate mode : Variable
Bit rate : 1 329 Kbps
Channel(s) : 2 channels
Sampling rate : 48.0 KHz
Bit depth : 24 bits
Stream size : 1.58 MiB (100%)
Writing library : libFLAC 1.2.1 (UTC 2007-09-17)

flac gives this warning - no idea if this is related to the one ffmpeg gives:

sample.WAV: WARNING: legacy WAVE file has format type 1 but bits-per-sample=24

[Carl Eugen Hoyos]

For future reports, please provide complete, uncut output of your ffmpeg-command (including the command line), third party application output is almost never needed.

FFmpeg warns that its flac-encoder does not support 24 (or 32) bit and the content was therefore down-sampled, so this is a feature request.

[Atrocia]

Ok, thanks for the reporting tip. I understand that this should be called a feature request, but I still suggest that in the interim there be a clearer warning - after all, flac is synonymous with lossless encoding. Doing lossy encoding, with only a somewhat obscure warning, could result in permanent data loss if the user doesn't keep the original file.

[Michael Niedermayer]

Ive added a better warning locally, will be in git with my next push

[dave rice]

The warning that Michael mentioned a year ago seems to no longer be enabled. Using an ffmpeg compiled from git on July 21, 2011 I would get a warning "Convertion will not be lossless'" in this scenario. In the latest git master 24 bit audio converts to 16 bit for flac encoding with no warning. pastebin here: ​http://pastebin.com/kGpT7fPj

[Carl Eugen Hoyos]

Please do not use external resources if you want to provide console output, but paste it here.

[holunder2]

Please check this patch by MakeMKV developer for 24 bit FLAC encoding: ​http://www.makemkv.com/download/ffmpeg/
I don't know if he has submitted the patch to ffmpeg, but it would very great if this would go upstream. :)

[Carl Eugen Hoyos]

I suspect this patch needs at least a copyright statement before it can be considered for inclusion.

[Michael Niedermayer]

Replying to cehoyos:

I suspect this patch needs at least a copyright statement before it can be considered for inclusion.

who should be credited as author if we merge something from this patch ?

[holunder2]

»This patch is Public domain. No copyright is claimed. Feel free to give a link to this page.« ​http://www.makemkv.com/forum2/viewtopic.php?p=23025#p23025

[Carl Eugen Hoyos]

Implemented by Justin.