Freaccmd: Unable to set a higher cbr bitrate than 160

[Flameborn]

Hello,

I am trying to split an m4b based on chapters and convert to CBR, 320 KBPS mp3. Despite what the help file says, the maximum bitrate seems to be 160 via the -b flag. Lower bitrates work as expected, e.g. 128.

I am using Intel MacOS 12.7.6.

Example command:

for f in *.m4b; do
  /applications/freac.app/Contents/MacOS/freaccmd -d "${f%.m4b}_out" --split-chapters -p "<track> <title>" -m cbr -b 320 "$f"
done

Any help is greatly appreciated.

[enzo1982]

Sorry for the late response!

The MP3 format supports bitrates above 160 kbps only for sample rates of 32 kHz or higher. For these sample rates, the format uses the MPEG 1 Audio Layer 3 profile which specifies bitrates up to 320 kbps.

When the sample rate is lower than 32 kHz, the MPEG 2 or MPEG 2.5 Audio Layer 3 profiles are used which support only up to 160 kbps.

As you seem to be dealing with .m4b audio book files and those often use lower sample rates, I think this might be what is causing the observed behavior here.

[Flameborn]

Thank you very much for your response. This is indeed what caused the issue. Would it be possible to add a warning and/or a switch when profile switching occurs? This would be quite useful to have since the encoded audio may not have the intended bitrate specified.

…

On 2025. Feb 12., at 23:53, Robert Kausch ***@***.***> wrote: Sorry for the late response! The MP3 format supports bitrates above 160 kbps only for sample rates of 32 kHz or higher. For these sample rates, the format uses the MPEG 1 Audio Layer 3 profile which specifies bitrates up to 320 kbps. When the sample rate is lower than 32 kHz, the MPEG 2 or MPEG 2.5 Audio Layer 3 profiles are used which support only up to 160 kbps. As you seem to be dealing with .m4b audio book files and those often use lower sample rates, I think this might be what is causing the observed behavior here. — Reply to this email directly, view it on GitHub <#641 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAHLD4EMBNEUQ7POHQH6VWT2PPGG7AVCNFSM6AAAAABQGFLOVWVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDMNJVGAYTONJZGA>. You are receiving this because you authored the thread.