如何从9个单声道输入文件生成9声道AAC编码音频文件？及如何创建最高64声道的MP4容器AAC编码音频文件？

Let's break down the issues with your original command and fix them step by step, including support for the high channel counts you mentioned (up to 64):

1. Fix the amerge Filter Syntax #

Your current filter only lists 2 input streams ([0:a][1:a]) but tells amerge to merge 9 inputs—this is a critical syntax error that would fail before even reaching the encoder limitation. You need to include all your input audio streams in the filter chain. For 9 inputs, that looks like:

ffmpeg -hide_banner -i 0.wav -i 1.wav -i 2.wav -i 3.wav -i 4.wav -i 5.wav -i 6.wav -i 7.wav -i 8.wav \
-filter_complex '[0:a][1:a][2:a][3:a][4:a][5:a][6:a][7:a][8:a]amerge=inputs=9[aout]' \
-map '[aout]' ...

For 64 inputs, you'd extend this pattern to include [0:a] through [63:a] and set amerge=inputs=64.

2. Resolve AAC Encoder Channel Limitation #

The default built-in aac encoder in FFmpeg doesn't support non-standard channel counts (like 9 or 64) out of the box, since standard AAC predefines layouts only up to 7.1 (8 channels). Here are two reliable workarounds:

Option 1: Use libfdk_aac (Recommended for Compatibility & Quality) #

The libfdk_aac encoder has excellent support for custom channel layouts, making it the best choice for non-standard multichannel audio. Specify the exact channel layout and set a suitable bitrate:

# For 9 channels
ffmpeg -hide_banner -i 0.wav -i 1.wav -i 2.wav -i 3.wav -i 4.wav -i 5.wav -i 6.wav -i 7.wav -i 8.wav \
-filter_complex '[0:a][1:a][2:a][3:a][4:a][5:a][6:a][7:a][8:a]amerge=inputs=9[aout]' \
-map '[aout]' -c:a libfdk_aac -channel_layout 9.0 -b:a 480k multichannel.m4a

# For 64 channels (example)
ffmpeg -hide_banner $(printf "-i %d.wav " {0..63}) \
-filter_complex "$(printf '[%d:a]' {0..63})amerge=inputs=64[aout]" \
-map '[aout]' -c:a libfdk_aac -channel_layout 64.0 -b:a 2048k multichannel_64ch.m4a

• -channel_layout N.0 explicitly tells the encoder to treat the stream as an N-channel custom layout
• Adjust -b:a (bitrate) based on quality needs—multichannel audio requires higher bitrates (e.g., 60k+ per channel for good quality)
• This works seamlessly for up to 64 channels, as both libfdk_aac and the MP4 container support these high channel counts

Option 2: Use Built-in aac with Experimental Mode #

If you can't use libfdk_aac (due to licensing or installation constraints), you can force the built-in encoder to handle non-standard channels by disabling strict compliance:

ffmpeg -hide_banner -i 0.wav -i 1.wav -i 2.wav -i 3.wav -i 4.wav -i 5.wav -i 6.wav -i 7.wav -i 8.wav \
-filter_complex '[0:a][1:a][2:a][3:a][4:a][5:a][6:a][7:a][8:a]amerge=inputs=9[aout]' \
-map '[aout]' -c:a aac -channel_layout 9.0 -strict experimental -b:a 480k multichannel.m4a

• -strict experimental allows the encoder to use non-standard AAC extensions
• Note: Player compatibility may be worse compared to libfdk_aac output, so test with your target playback system first

3. Verify Your Output #

To confirm the channel count is correct, run this command to inspect the file's metadata:

ffmpeg -i multichannel.m4a -hide_banner

Look for a line like:

Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, 9.0, fltp, 479 kb/s

This confirms your 9-channel AAC stream is properly embedded in the MP4 container.

内容的提问来源于stack exchange，提问作者Thomas Bratt