m4a editors?

[bat999]

Question withdrawn.

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and I want to know if there's a similar utility for WAV files.

Also MP3DirectCut can do fadein/fade out without re-encoding (so I've read), so I wondered if that was there for WAV as well.

[Baldrick]

I have not seen any simple lossless m4a/aac editor with a gui.

[bat999]

I have not seen any simple lossless m4a/aac editor with a gui.

Thanks Baldrick for the no-nonsense reply.

[poisondeathray]

can you mux with blank video into mp4 and use avidemux? (then extract aac audio)

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I've used MKVMerge for splitting audio files but most of the time the split isn't exacting, i.e. I don't get the required accuracy in milliseconds.

[Gavino]

can you mux with blank video into mp4 and use avidemux? (then extract aac audio)

I've used MKVMerge for splitting audio files but most of the time the split isn't exacting, i.e. I don't get the required accuracy in milliseconds.

Using video software to edit audio, you will not get an accuracy greater than the duration of 1 (video) frame.

To get millisecond accuracy, you need to have a framerate of 1000fps, so for example with pdr's suggestion you would use a blank clip with that rate.

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how do i create/get a blank clip with that rate?

I tried but your can't alter FPS in MKVMerge.

[dylz]

Goldwave opens and edits m4a but doesn't output back to it.

[poisondeathray]

how do i create/get a blank clip with that rate?

I tried but your can't alter FPS in MKVMerge.

you can generate a blank clip with avisynth , and encode using vdub for example

e.g
blankclip(length=10000, width=16, height=16, pixel_type="YV12", fps=1000)

Adjust the parameters to whatever you want. When encoding, if you use I-frame only encoding, you can cut on any frame with video editing software

[Gavino]

Another thought that occurs to me is that most compressed audio formats also have what is the equivalent of GOPs (confusingly, for those used to video terminology, called 'frames'), so there is a limit on the granularity of any lossless editing you can do.

For example, MPEG audio (eg mpa) uses frames of 576 samples (about 13ms at 44.1KHz).

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Thanks poisondeathray, I try what you said and let you know.

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Okay, I did it and encoded a blank video with 1000fps using MeGUI. But how do I encode with I-frames only? Because I'm still not getting accuracy.

[poisondeathray]

what compression are you using ?

if you are using x264 encoder, set --keyint 1

[Gavino]

Okay, I did it and encoded a blank video with 1000fps using MeGUI. But how do I encode with I-frames only? Because I'm still not getting accuracy.

How accurate do you want the audio cutting to be?
Once you get the I-frames sorted out, you will still have to take into account my point about audio 'frame' size. AAC can have a block size as large as 1024 samples (which is over 20ms, even at 48KHz).
http://en.wikipedia.org/wiki/Advanced_Audio_Coding#How_AAC_works

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Ok, I looked into that link you posted but could only understand a little. My knowledge of waves in physics isn't at an advanced level. However, I understood your GOP equivalent concept for audio streams. Btw, I'm trying to split WAV audio, and I want millisecond accuracy.

I've tried poisondeathray's suggestion. I messed around, tweaked and altered the syntax here and there but no avail.
For example, when I fed the AVS script into x264, the output video ended up having 2000fps (twice of that specified in the script); so I changed it to 500fps and then x264 encoded it to 1000fps. And when I open the video in MediaInfo, it shows two fields,
frame rate: 500fps
original frame rate: 1000fps

Anyways, I wasn't able split the file accurately. The desired output WAV segment should've been 34.532s but I got 34.600s.

[Gavino]

I don't know why your script didn't work, but if you are working with WAV audio, you would be better using a dedicated audio editor like Audacity (free). This should allow sample accuracy when cutting and since WAV is uncompressed, there is no re-encoding involved.

I thought your source was m4a/aac (though I see now you mentioned WAV in your first post). The idea of using a blank clip was simply a means to get your source into a video editor for lossless cutting, as there are no audio editors (as far as we know) that can do that for m4a/aac. But for WAV, any audio editor worthy of the name can do it.

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In fact, my first solution to splitting the audio was by using Audacity; but then I was like "Oh wait, I'll lose quality if I do it this way!"

You're right. That fact you mentioned totally went over my head at that time.

Anyways, thanks a lot for your time and suggestions.