<p>AC3 doesn't support 7.1.  Only took like 25 hours of messing with the filter chain to figure it out.</p>

CC BY-SA 4.0
2023-06-27T23:18:40.103Z
2023-06-27T23:18:40.103Z
Bryan Austin
<p>I am trying to reconstruct a 7.1 channel output after processing, and ffmpeg keeps outputting a <code>5.0(side)</code>. (trimmed for readability)</p>
<pre><code>ffmpeg -i &quot;intermediate/refined.mka&quot; -i &quot;intermediate/extracted.data&quot; -filter_complex &quot;\
...
[ml9][mr9][mc2][ms1][mm2][mt2][mw2][me2]amerge=inputs=8,aformat=channel_layouts=7.1[out]&quot; -map &quot;[out]&quot; &quot;intermediate/mixed.mka&quot;
</code></pre>
<p>Output:</p>
<pre><code>...
Input #0, matroska,webm, from 'intermediate/refined.mka':
    Stream #0:0: Audio: wavpack, 44100 Hz, stereo, fltp
...
Input #1, dts, from 'intermediate/extracted.data':
    Stream #1:0: Audio: dts (DTS-HD MA), 48000 Hz, 7.1, s32p (24 bit)
...
Output #0, matroska, to 'intermediate/mixed.mka':
    Stream #0:0: Audio: ac3 ([0] [0][0] / 0x2000), 48000 Hz, 5.0(side), fltp, 448 kb/s
</code></pre>
<p>I am feeding 8 mono channels into <code>amerge</code> and adding the 7.1 <code>aformat</code> constraint, and it gives me a 5.0 without warning or error. By everything I've read in the docs <code>amerge</code> should only add channels, never discarding them. Any idea what's going on here?</p>

<ffmpeg>
ffmpeg amerge ignoring channel layout
Bryan Austin
# ffmpeg amerge ignoring channel layout

(Asked by: username_0 on 2023-06-18)

I am trying to reconstruct a 7.1 channel output after processing, and ffmpeg keeps outputting a 5.0(side). (trimmed for readability)
ffmpeg -i "intermediate/refined.mka" -i "intermediate/extracted.data" -filter_complex "\
...
[ml9][mr9][mc2][ms1][mm2][mt2][mw2][me2]amerge=inputs=8,aformat=channel_layouts=7.1[out]" -map "[out]" "intermediate/mixed.mka"

Output:
...
Input #0, matroska,webm, from 'intermediate/refined.mka':
    Stream #0:0: Audio: wavpack, 44100 Hz, stereo, fltp
...
Input #1, dts, from 'intermediate/extracted.data':
    Stream #1:0: Audio: dts (DTS-HD MA), 48000 Hz, 7.1, s32p (24 bit)
...
Output #0, matroska, to 'intermediate/mixed.mka':
    Stream #0:0: Audio: ac3 ([0] [0][0] / 0x2000), 48000 Hz, 5.0(side), fltp, 448 kb/s

I am feeding 8 mono channels into amerge and adding the 7.1 aformat constraint, and it gives me a 5.0 without warning or error. By everything I've read in the docs amerge should only add channels, never discarding them. Any idea what's going on here?

**Tags:** ffmpeg


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## 1 answers

### Answer by username_0 on 2023-06-27. Score: 0 | Accepted answer

AC3 doesn't support 7.1. Only took like 25 hours of messing with the filter chain to figure it out.


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