Audio
1.Process/Copy mode
Copy mode
In that mode, avidemux will just copy the audio source (external/avi/...) to the output. It is used when you just cut an avi for example or change the audio track.That also applies to mpeg encoding/transcoding/requantizing.
Process mode
Avidemux will first decompress the audio, then apply the filters if any. If you don't set any filters, you will end up with a huge wav file as audio track.
To be used, the corresponding audio codec must be present on your system. See input format.
When using Audio->Save audio, the audio is saved depending on the current mode. If the mode is set to copy, you will save a raw AC3/MP3/WMA... track. In process mode, the file will be processed then saved
It can be useful to encode a track in MP2 to create a video CD for example. You will end up with a .m1v video elementary stream and a .mp2.
2.Filters
Normalize
That filter normalize linearily the audio. It helps if the overall volume is very low (for example from ac3 audio track).
Convert to 44.1 khz
That filter does the 48->44.1khz conversion. If the input is not 48 khz, it does nothing .
It is based on wavefs44, borrowed from DVD2AVI.
Time shift
This filter shifts the audio by removing the beginning or duplicating to create new sound. The value entered is the shift in ms.
It is the only filter to work also in copy mode. Very handy to correct a sync error on avi or mpeg file.
Resample to
This filter resamples the audio to the user given frequency. It is faster than the 48->44.1 but may be of lower quality. It is based on a slightly modified sox engine.
Pal2Film and Film2Pal
If you want to alter a video and change its fps from film (23.976) to pal (25) you have to use the film2pal filter on audio stream to keep audio/video sync. The opposite is true for pal to film encoding.
Channels
Allow you to switch from mono to stereo. It is sometimes needed as for example, mono audio is illegal for VCD.
3.Encoder Filters
These filters are just like regular filters, but they do output compressed audio.
Uncompressed
MP3
Based on liblame. You can select the bitrate and mode (joint stereo or stereo). For mono, it will be automatic.
It encodes in CBR and VBR modes
Ffmpeg mpeg audio
This is lavcodec mpeg audio encoder.
It encodes only in CBR mode (and no joint stereo, even if there is an entry in the dialog). It is declared suitable to use as DVD audio track.
Ffmpeg AC3
Also from libavcodec.
It encodes stereo AC3 files. Never tried to see if the resulting AC3 is acceptable by an hardware decoder
Toolame (internal)
This is using a preversion of toolame that is a library and thus usable directly by avidemux without piping.
From 2.0.24 and after, it is suitable to use as VCD/DVD audio track
4.Use case
Avi with WMA audio
Say you have an avi with WMA audio and want to convert it to MP3.
Load your avi, let the video to copy as we won't modify it.
Set the audio to process and select MP3 codec, Audio->Audio codec
Select Audio->configure codec, set 128kbps j-stereo
File->save avi, and voila you just converted the audio track.
Avi with 44.1 Khz mp3 audio to DVD
In that case, we will select process mode, resample to 48 khz and ffmpeg mpeg audio.
The audio track will be first decompressed to PCM, then upsampled to 48 Khz and finally compressed to mpeg audio
You can then use Audio-save audio to get the .mp2 file, or use File-Save as DVD PS to directly save it as a mpeg containing both audio and video. This mpeg is suitable to dvd authoring directly.
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