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  1. For a multimedia playback system I need to encode multichannel sound files as AC3.

    I managed to run the ffmpegx encoder, but when I convert back to multichannel PCM (using QuickTime Pro 7), it seems that the input channels have been mixed together to the first two (stereo front) channels, while the other four channels are empty.

    I am using a 6-channel 48 kHz 16-bit WAV file as input. This is accepted by ffmpegx, saying it is "5.1". I use AC3 as target, encode-audio only. Audio-tab says:

    - 448 kbit/s, 48000 Hz, 5:1 channels, CBR, Audio track: 0 (what is this supposed to mean?), Inverted mapping yes (that's the default).

    What am I doing wrong? I can adjust the channel mapping of my source file, no problem, but I need the 5 or 6 input channels to correspond exactly with separate channels in the AC3 file.

    Perhaps related: I have no clue what the "Audio track" selection menu in the Audio tab is supposed to mean, neither what the "Add audio..." button is for.

    Thanks very much!
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  2. Think I solved the issue. First of all, QuickTime Player 7 although supporting multi-channel audio when using PCM files, seems to have broken or incompatible A3 decoding. Second, I am using Audacity now for export. It uses ffmpegx as backend, but is more comfortable than the ffmpegx standalone app, because it has a channel mapping matrix and can go up to 640 kbps.

    Files exported this way with Audacity are played correctly back as 5 / 6 discrete channels with VLC.
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  3. Explorer Case's Avatar
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    Feb 2004
    Middle Earth
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    Originally Posted by Britzel View Post
    Audio track: 0 (what is this supposed to mean?)
    That number is the stream number. For files that have multiple audio streams (e.g. multiple languages), this is where you may select which stream to use. Numbering starts with 0 for the first detected stream.
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