What audio formats are recognized to replace the audio track? I tried with aac but it gives me error. If I export the audio track Avidemux save the file with the .aac extension but the real format is not MPEG-4 but ADTS.
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Avidemux doesn't support audio-only MP4 files, it expects ADTS- or LATM-encapsulated AAC streams as an external audio track. It exports AAC in an ADTS envelope (as AAC is useless without extradata and extradata is not a part of the stream).
Other than "raw" (ADTS-encapsulated) AAC, Avidemux supports WAV (16 and 24-bit), MP2, MP3, AC3, E-AC3 ans DTS. Max. # of channels: 8.