I am trying to encode some sound on Ubuntu 12.04 Linux. I need to use libfaac (using version 1.28) for encoding, and I want to encode with a very low bit rate - the total amount, including the overhead of the transport stream, should be below 64 Kbps. Audio Input: PCM, 48 kHz, 2 channels, s16, 1536 kbps
Using the faac command-line tool, I get the output below by encoding 5 minutes of audio - so there is enough time for the bitrate to average. I can't get it to go below 64 Kbps, or above 165 Kbps for that matter. I tried to set some other parameters, but to no avail. When I set the bitrate> 64, it works fine. Looking through the libfaac code, I do not see these restrictions being imposed.
$ ./faac -b 40 -w -o /tmp/yellow-audio-40k.mp4 /tmp/yellow-audio.wav Freeware Advanced Audio Coder FAAC 1.28 Average bitrate: 64 kbps Quantization quality: 100 Bandwidth: 5442 Hz Object type: Low Complexity(MPEG-4) + M/S Container format: MPEG-4 File Format (MP4) Encoding /tmp/yellow-audio.wav to /tmp/yellow-audio-40k.mp4 frame | bitrate | elapsed/estim | play/CPU | ETA 14063/14063 (100%)| 64.2 | 10.7/10.7 | 27.91x | 0.0
$ mediainfo /tmp/yellow-audio-40k.mp4 General Complete name : /tmp/yellow-audio-40k.mp4 Format : MPEG-4 Format profile : Base Media / Version 2 Codec ID : mp42 File size : 2.35 MiB Duration : 5mn 0s Overall bit rate mode : Variable Overall bit rate : 65.7 Kbps Encoded date : UTC 2012-12-05 00:03:38 Tagged date : UTC 2012-12-05 00:03:49 Writing application : FAAC 1.28 Audio ID : 1 Format : AAC Format/Info : Advanced Audio Codec Format profile : LC Codec ID : 40 Duration : 5mn 0s Bit rate mode : Variable Bit rate : 64.2 Kbps Maximum bit rate : 73.7 Kbps Channel(s) : 2 channels Channel positions : Front: LR Sampling rate : 48.0 KHz Compression mode : Lossy Stream size : 2.30 MiB (98%) Language : English Encoded date : UTC 2012-12-05 00:03:38 Tagged date : UTC 2012-12-05 00:03:49
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