Hi
I'd like to use the dual-channel (or dual-stereo) mode encoding to record two monophonic tracks which must be synchronized (delays less than 100 ms are acceptable).
I'd like to know how the MP3 frames are created in this mode, and especially if I will be able to easily split the files into two monophonic tracks if needed. In other works, does each MP3 frames contains the two (mixed) tracks, or only one track (assuming the other track is encoded in the next frame, etc.) in this mode ?
I couldn't find much documentation on the dual-channel mode. Any pointer, please ?
Thanks
Full Version: Dual channel (dual stereo) mode
QUOTE(Efcis @ Nov 19 2007, 01:12) 
I'd like to know how the MP3 frames are created in this mode
lame -md
QUOTE(Efcis @ Nov 19 2007, 01:12)
, and especially if I will be able to easily split the files into two monophonic tracks if needed.
No, it's not easy.
QUOTE(Efcis @ Nov 19 2007, 01:12)
In other works, does each MP3 frames contains the two (mixed) tracks, or only one track (assuming the other track is encoded in the next frame, etc.) in this mode ?
A dual-channel stream is like a normal stereo stream. It's one stream with 2 channels and not two streams interleaved on a frame level.
HTH,
SG
small addition to what Sebastian said:
when using dual-channel each channel wil get half of the bitrate, in a "normal"stereo stream the encoder may vary the bitrate allocation of each channel according to its complexity.
when using dual-channel each channel wil get half of the bitrate, in a "normal"stereo stream the encoder may vary the bitrate allocation of each channel according to its complexity.
QUOTE(Sunhillow @ Nov 19 2007, 13:57)
small addition to what Sebastian said:
when using dual-channel each channel wil get half of the bitrate, in a "normal"stereo stream the encoder may vary the bitrate allocation of each channel according to its complexity.
One more small addition...If you want to avoid any cross talk between the channels then do not use joint stereo (-mj) but instead use full stereo (-ms).
QUOTE(pdq @ Nov 19 2007, 20:11)
QUOTE(Sunhillow @ Nov 19 2007, 13:57)
small addition to what Sebastian said:
when using dual-channel each channel wil get half of the bitrate, in a "normal"stereo stream the encoder may vary the bitrate allocation of each channel according to its complexity.
One more small addition...If you want to avoid any cross talk between the channels then do not use joint stereo (-mj) but instead use full stereo (-ms).
Will that matter? Surely if the channels are dissimilar, -mj will still result in L/R frames, instead of M/S frames.
I suppose crosstalk between stereo channels can't be noticed as easily compared to listening each channel individually.
QUOTE(Sunhillow @ Nov 19 2007, 18:57)
when using dual-channel each channel wil get half of the bitrate, in a "normal"stereo stream the encoder may vary the bitrate allocation of each channel according to its complexity.
Are you sure about that?
The mp3 format certainly doesn't coerce encoders to do a strict 50/50 bit allocation.
Cheers!
SG
QUOTE(SebastianG @ Nov 20 2007, 10:37)
QUOTE(Sunhillow @ Nov 19 2007, 18:57)
when using dual-channel each channel wil get half of the bitrate, in a "normal"stereo stream the encoder may vary the bitrate allocation of each channel according to its complexity.
Are you sure about that?
The mp3 format certainly doesn't coerce encoders to do a strict 50/50 bit allocation.
Cheers!
SG
I believe that is just a characteristic of lame's implementation of that switch. I doubt that it is used very often.
QUOTE(SebastianG @ Nov 20 2007, 15:37)
Are you sure about that?
The mp3 format certainly doesn't coerce encoders to do a strict 50/50 bit allocation.
I'm quite sure I read this somewhere. The difference between simple stereo and dual channel is the fixed bit allocation for each channel. ISO 11172-3 only describes the decoder and here the two non-joint stereo modes are not different.
At least the german Wikipedia article on LAME also writes that both channels use the same allocation. But everyone can write everything there...
From the Lame documention:
Nothing to see here kids, time to move along.
QUOTE
dual channels
In this mode, the 2 channels will be totally independently encoded. Each channel will have exactly half of the bitrate. This mode is designed for applications like dual languages encoding (ex: English in one channel and French in the other). Using this encoding mode for regular stereo files will result in a lower quality encoding.
In this mode, the 2 channels will be totally independently encoded. Each channel will have exactly half of the bitrate. This mode is designed for applications like dual languages encoding (ex: English in one channel and French in the other). Using this encoding mode for regular stereo files will result in a lower quality encoding.
Nothing to see here kids, time to move along.
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