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Topic: Should fb2k report bits per sample for ffmpeg-generated lossy-in-Matroska? (Read 745 times) previous topic - next topic
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Should fb2k report bits per sample for ffmpeg-generated lossy-in-Matroska?

Played around with remuxing .opus into .mka , and found that foobar2000 reports them as 32 bits. Repeated with AAC and Vorbis: 32. (Same with webm.) Repeated with an .mp3: 16, so it is not consistent.

Then I dug up some old (-> might be older ffmpeg?) Matroska files with AAC, and found them to be reported as 16.

For all that I know, ffmpeg could write misleading information to the container. Tried ffmpeg 4.0.2 and 3.4. Could anyone reproduce?

Re: Should fb2k report bits per sample for ffmpeg-generated lossy-in-Matroska?

Reply #1 –
If ffprobe reports bit-depth you will see it in the properties. I turned a test m4a file into mka with MKVToolNix GUI and bitdepth was reported as zero by ffprobe and foobar didn't show any incorrect info either.

Re: Should fb2k report bits per sample for ffmpeg-generated lossy-in-Matroska?

Reply #2 –
I created mkv with aac audio in ffmpeg 4.0.2 and foobar reported bitdepth as 32. But no bitdepth is reported for mkv created with MKVToolNix. So, yes, it seems that ffmpeg is writing misleading information to the container.

Re: Should fb2k report bits per sample for ffmpeg-generated lossy-in-Matroska?

Reply #3 –
ffprobe found no bitdepth info in what I tried before the original posting, and no bitdepth info in what I tried right now.  So whatever ffmpeg writes is not anything ffprobe knows about, and that smells like a bug?

So after the replies from Case and Rollin, I followed up with this test:
* MKVToolNix-remuxed the offending .mka into a new .mka. fb2k finds no bit-depth of that.
f* fmpeg-remuxed the latter new .mka into .mka. fb2k reports bit-depth.
* Tried to use MP3Tag to remove the tags from the new mka. fb2k still reports bit-depth.
* Tried to use fb2k to remove tags. fb2k still reports bit-depth.

Tried ffprobe on the result. There are still Matroska chapters with chapter names (= track titles), and - even though it has been through ffmpeg - there is still metadata added by MKVToolnix (like:       _STATISTICS_WRITING_APP-eng: mkvmerge v26.0.0 ('In The Game') 64-bit
      _STATISTICS_WRITING_DATE_UTC-eng: 2018-09-20 15:13:16
and so on).