Extracting WMA channels

[zuja9]

Hello!

I have an iRiver E100 that is capable of recording audio from its built-in microphone, external microphone and line-in. Most of the time I make recordings with its built-in one which is mono, though the format it's recording is a Stereo WMA, 192kbps and it's a waste of disk capacity, since both audio tracks contain the same material. There is no option adjusting the channels for recording.

I'm looking for a (command line if there's one) tool that can extract one channel from a WMA file and save to another. For instance my 192kbps WMAs consist two 96kbps WMA audio streams, one for each channel (2). I'd like to extract one of these channels to a new file, that'd be Mono and 96 kbps.

Thanks in advance
Zooya

[olyteddy]

Are you sure they are two discrete channels, and not a sum channel (L+R) and a difference (L-R) channel? If they are sum and difference, Mono uses almost no additional space as the difference channel will be basically null.

[zuja9]

Are you sure they are two discrete channels, and not a sum channel (L+R) and a difference (L-R) channel? If they are sum and difference, Mono uses almost no additional space as the difference channel will be basically null.

Good question, I haven't been able to figure this out yet since no application I know gives me this information, but I'm pretty sure it's not stored that way. For example, I have a recording, speech-of-my-friend-in-the-school.wma that is 11 682 672 in bytes and 8:04 long (484 seconds). At 192kbps a 484 seconds long audio clip would be (192000*484)/8 = 11 616 000 bytes which is almost the same as the real size (maybe there are more frames than exactly 484 seconds and the real bitrate doesn't end with 000, there's a header, that's why the real size is bigger), so I don't think it spares disk space by summing/differencing audio tracks, because in this case the size should be around half as big as a conventional 192kbps clip.

[olyteddy]

Can they play in WinAmp? WinAmps SendTo -> Format Convertor has WMA as an option and allows you several Mono format choices, including a 'Voice' profile.

[INFRATOM]

Do you have any audio editing software they all do that, save as then select mono. I guess there are free ones too.

[zuja9]

I have WinAmp and audio editing softwares, but I would not like to convert my clips anyways. I could downmix them and convert them using ffmpeg/lame/etc. but this will result in the loss of quality. The only option for me is copying one channel and saving it as a mono-channel WMA.

In the meantime I've found AsfBin, but couldn't figure out how to separate a stereo audio tracks into two mono channels without re-encoding. Tried: asfbin -i <inputfile> -o <outputfile> -nostream 2 , but it handles the audio part as one stream.

Also tried with ffmpeg -i <inputfile> -ab 96k -ac 1 -acodec copy <outputfile>, no success, it generates an output file arund the same size and bitrate as the input.

[zuja9]

Anyone who could help?

[poisondeathray]

Unlikely that you can just extract a channel and magically cut the size in half. You have to probably re-encode it.

WMA is a closed, and proprietary format, you will need a license to manipulate. e.g. Adobe Auditon supports WMA, but I tested what you wanted to do , and it re-encodes as well

You can't even do what you want with open source formats that have lots of support, like mp3, aac. etc. they all re-encode, or use a wav intermediate then re-encode. - so the likelihood of it working with wma is even less

It is likely that you have a duplicate i.e. the L+R channels are duped so it is a fake stereo. You can look at the waveform in Audition for example, to check if channels are different.

[zuja9]

WMA is a closed, and proprietary format, you will need a license to manipulate. e.g. Adobe Auditon supports WMA, but I tested what you wanted to do , and it re-encodes as well

Well, yes it's closed, but I'm hoping there is someone (or some company) who bought this license and wrote an application that enables these things. Adobe had never been famous about their applications allowing these kinds of low-level (or fine) hacks, they don't care about disk space and CPU-usage at all. If you have to deal with multimedia, get prepared and pay for large hard drives and waste it if needed :P That's what they believe and I don't really.

Btw, could you try me looking for an option like enable smart rendering, because as far as I know it's about copying streams if possible. If you find it turned off, please turn it on and try again what you did.

It is likely that you have a duplicate i.e. the L+R channels are duped so it is a fake stereo. You can look at the waveform in Audition for example, to check if channels are different.

I have already checked it, I'm sure I've also written about that earlier. It's a fake stereo, two channels that are the same (except the noise, because the input is stereo, only the built-in microphone is mono).

Still don't want to re-encode and looking for a solution

[zuja9]

Anyone here?