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AIFF 48kHz/24-bit

Anatoli Babenia's photo
Anatoli Babenia
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2 min read

AIFF is a file format, which is also a standard way to exchange audio when making movies. When video footage and sounds are recorded, the film post-production starts, and AIFF provides a way to send uncompressed audio to editors.

Recording sound outside the studio usually involves several mics and a "digital audio recorder" device like Zoom. My rather Zoom H1 Handy Recorder writes WAV and MP3, but no AIFF. During filming session I recorded WAV as 96kHz/24-bit, and now I need convert that to AIFF. Some records are done with stereo mic, and some with mono mic, so I also need to convert records with only left channel to mono.

The ffmpeg command I used to downsample all 96kHz WAV in a directory to AIFF.

for i in .WAV; do ffmpeg -i "$i" -c:a pcm_s24be -ar 48000 \
  "${i%.}.aiff"; done

This still produces stereo files. I added -af "pan=mono|FC=FL"param to do mono output and map Front Left channel to Front Center.

for i in .WAV; do ffmpeg -i "$i" -c:a pcm_s24be -ar 48000 \
  -af "pan=mono|FC=FL" "${i%.}.aiff"; done

I also want to copy original metadata to AIFF.

$ ffprobe S1K8D1.WAV -hide_banner 
Input #0, wav, from 'S1K8D1.WAV':
  Metadata:
    encoded_by      : ZOOM Handy Recorder H1
    date            : 2022-04-05
    creation_time   : 15:43:50
    time_reference  : 5436480000
    coding_history  : A=PCM,F=96000,W=24,M=stereo,T=ZOOM Handy Recorder H1
  Duration: 00:00:27.53, bitrate: 4617 kb/s
  Stream #0:0: Audio: pcm_s24le ([1][0][0][0] / 0x0001), 96000 Hz, 2 channels, s32 (24 bit), 4608 kb/s

For that I had to specify -write_id3v2 1 param.

for i in .WAV; do ffmpeg -i "$i" -c:a pcm_s24be -ar 48000 \
  -af "pan=mono|FC=FL" -write_id3v2 yes "${i%.}.aiff"; done

Some notes.

  1. I could not validate that there is no right channel before processing.

  2. Metadata was not updated after recoding. Ideally reencoder should add another line to coding_history (BEXT CodingHistory).

  3. Updated AIFF-C/sowt format allows little-endian encoding of samples, which should save some memory. Need to research how to create it.

audiofilmmakingaiffpost-production