Decoding WMAP audio codecs with VirtualDub

[Mark53]

Hello,

I use VirtualDub2 (build 44282) and when I try to compress a WMV file with x265 for the video and mp3 for the audio, the resulting file won't have audio at all. It seems that VirtualDub cannot decode WMAP audio codecs (even though no error is popping up). I installed the AC-3 ACM codec by FCCHANDLER, but it didn't solve the issue… What is the right procedure to follow?

After some investigation, it seems that it's the 32-bit audio streams that VirtualDub cannot decode. The fact is only 8-bit and 16bit appear in the Audio compression interface… Is it a lost cause?

Regards,
Mark

[LigH.de]

VirtualDub2 supports what its ffmpeg input module can handle. Loading WMV, it will not use the ACM codecs.

I doubt that a "32-bit resolution" is the reason, it should be able to handle audio decoded to floating point formats. It might rather be a multi-channel layout. MP3 does not support 6 channels, at most 2. But we don't know for sure, you did not provide a MediaInfo analysis of your clip, so we can only guess what's in your WMV.

[Mark53]

Well, I thought of this 32-bit thing because when I try to save the audio data, I get the following error message:
Cannot resample audio: the source audio format is not supported (must be 8-bit or 16-bit PCM)

But I found out that no clip with MPEG AAC audio can be decoded. There must be a codec missing to decode this very classic format! Most of my MP4 files use it...

The problem occurs with any basic WMV file, but if you want, here is an analysis made with MediaCoder:

General
Complete name : C:\Temp\Video1.wmv
Format : Windows Media
File size : 181 KiB
Duration : 12 s 32 ms
Overall bit rate mode : Constant
Overall bit rate : 123 kb/s
Maximum Overall bit rate : 103 kb/s
Movie name : CNN C1
Performer : migdom
Encoded date : UTC 2004-05-11 15:45:28.968
Copyright : 5/11/2004

Video
ID : 2
Format : WMV1
Codec ID : WMV1
Codec ID/Info : Windows Media Video 7
Description of the codec : Windows Media Video V7
Duration : 12 s 33 ms
Bit rate mode : Constant
Bit rate : 80.0 kb/s
Width : 320 pixels
Height : 240 pixels
Display aspect ratio : 4:3
Frame rate : 30.000 FPS
Nominal frame rate : 15.000 FPS
Bit depth : 8 bits
Bits/(Pixel*Frame) : 0.035
Stream size : 118 KiB (65%)
Language : English (United States)
Duration_Source : General_Duration

Audio
ID : 1
Format : WMA
Format version : Version 2
Codec ID : 161
Codec ID/Info : Windows Media Audio
Description of the codec : Windows Media Audio 9 - 16 kbps, 16 kHz, mono (A/V) 1-pass CBR
Duration : 12 s 32 ms
Bit rate mode : Constant
Bit rate : 16.0 kb/s
Channel(s) : 1 channel
Sampling rate : 16.0 kHz
Bit depth : 16 bits
Stream size : 23.5 KiB (13%)
Language : English (United States)
Duration_Source : General_Duration

[LigH.de]

As already mentioned: Per default, VirtualDub2 uses the ffmpeg input plugin, which should contain all required codecs implemented by the ffmpeg project. That doesn't mean it supports every codec which exists in the world, though... e.g. AAC may be supported in the LC flavour, but not in the HE flavour. And WMA audio may not be supported in the extremely low 16 kbps bitrate variant. In such cases it may be helpful to test if another input plugin helps or if decoding via an AviSynth script closes the gap.

Furthermore, I'm waiting for a VirtualDub2 update to make it support AV1 video decoding. Its author knows about my request but seems to be somewhat busy...

[Mark53]

Sure, but I'm talking about very classic and windespread formats here (WMAP and MPEG AAC), there should be a codec out there to decode them with VirtualDub… I installed AC3ACM plugins but it didn't solve the problem.

Plus, I'm not tight with VirtualDub2 so I'm open to any other VirtualDub variant. How do you, guys, recompress a video with MPEG AAC audio?

[LigH.de]

I believe you miss a few important points here...

First of all, the difference between decoding and encoding. If you want to create a video with AAC audio, you need an AAC encoder, not an AAC decoder. And if you have a clip with WMA audio stream, you need a WMA decoder, not an AAC decoder and neither an AC3 decoder.

If VirtualDub2 uses the ffmpeg input plugin, it uses no ACM codec installed in your system. It doesn't need to. So installing AC3ACM doesn't matter. Especially because AC3 is neither to be decoded nor to be encoded.

In addition, read the error message:

Cannot resample audio: the source audio format is not supported (must be 8-bit or 16-bit PCM)

The issue here seems to be the resampler, the piece of code which should calculate from the unsupported sampling frequency of 16 kHz to a sampling frequency supported by the AAC encoder. The chain from the WMA decoder via the resampler to the AAC encoder doesn't seem to work here. Means, the codecs are possibly not the main problem. So it may not help to fiddle more with the codecs.

I believe that the problem for VirtualDub2 is to calculate from 16 kHz to 44.1 or to 48 kHz in the middle of the conversion. Just a guess. I am not sure.

[Mark53]

I'm only talking about decoding issues here. All I want is compress these audio streams to mp3 (and a mp3 encoder is already shipped with VirtualDub2, so encoding is not an issue). At the moment, my version of VirtualDub cannot decode some audio streams (namely WMAP and MPEG AAC) and when I run a compression to mp3 (which produces no sound in the resulting video), no error is popping up, which looks like a bug.

I don't know much about VirtualDub internals but from what I understood, putting plugins in the right directories enables VirtualDub to load them at run time, so it's always possible to add new plugins. Now, I confess I don't know whether they are used for encoding or decoding.

The audio streams mentioned above being very common, I can't believe corresponding plugins for VirtualDub don't exist… Once again, how do you do, guys? Which version of VirtualDub do you use?

[LigH.de]

AAC is not AAC. Well possible that the ffmpeg input plugin can decode LC-AAC, but not HE-AAC. And well possible that you need to check some options here and there to help converting the decoded audio to a format which is supported by the following encoder, if it does not support the decoded format without an additional conversion.

I mentioned your issue in the doom9 forum where the developer(s) of VirtualDub2 can be found. Please have a little patience, I hope more replies will arrive later...

[jagabo]

VirtualDub2 has the ability to read and decompress WMA v2 and includes the ffmpeg lame mp3 encoder. It also has no problems with AAC LC. Not sure about AAC HC.


[Attachment 53637 - Click to enlarge]

The older versions of VirtualDub (non-2) would not read WMV files at all without a third party plugin. The original author was threatened with a lawsuit by Microsoft long ago when he first introduced WMV support. So he removed it and, for as long as he maintained the program, never added it back.

[Mark53]

I had a quick look at wikipedia, and it seems that AAC is more efficient than MP3, I didn't know that. So, instead of converting the audio stream to MP3, I could as well keep the original sound. But for that, I still need a decoder.

Oh, thank you, that was very nice of you to post on doom9 forum on my behalf. The fact is that I registered on that forum too but I couldn't find topics about VirtualDub issues, so I preferred posting here.

[Mark53]

@jagabo where did you get the decoder? For instance, if I recompress this small wmv video (http://www.lehman.edu/faculty/hoffmann/itc/techteach/video/Video1.WMV), I lose the sound.

[jagabo]

The aac decoder (ffmpeg) is included in VirtualDub2. Try forcing the ffmpeg video decoder when you open the WMV file via the "Files of Type" pulldown, in case you have some other decoder with a higher priority.

[Mark53]

To my knowledge, the dropdown you mentioned was accessible in the "Audio from other file..." menu. So, I chose the same file (which looks quite unusual) and selected "FFMPeg: audio", then compressed the video. I still have no sound.

[jagabo]

To my knowledge, the dropdown you mentioned was accessible in the "Audio from other file..." menu. So, I chose the same file (which looks quite unusual) and selected "FFMPeg: audio", then compressed the video. I still have no sound.

Importing that way works for me. The version I'm using:


[Attachment 53640 - Click to enlarge]

If you want to make your file available I'll try it here. Here's the WMV file I was testing with.

[Mark53]

My VirtualDub2 version is a little bit more recent than yours (build 44282).

That's it, I finally understood what didn't work! I used to convert the sampling rate of the audio streams to 44KHz (it's a habit I took when using VirtualDubMod because otherwise I noticed time shifts in the sound). If I remove the conversion, that works, the final file keeps sound. But if I perform the conversion, the sound disappears (only for WMAP and AAC sound formats).

Maybe I should report the bug to the VirtualDub authors (on doom9 forum?).

[jagabo]

Audio conversion and compression worked for me with these settings:


[Attachment 53642 - Click to enlarge]

[Mark53]

Good point. Converting to 16-bit works but with "no change", it does not:

[Attachment 53643 - Click to enlarge]
Strangely, it seems that the original audio Stream is already encoded in 16-bit.

[davexnet]

Did you set Audio/full processing mode ?

[Mark53]

Sure, since I'm converting the Stream to MP3.

[shekh]

Hi, I confirm the bug.
The audio conversion (resampling) needs some work but also disappeared error message is a problem too.