Edit AC3 header?

[Barleyman]

I have an AC3 file that the mediainfo, eac3to and others insist is a stereo 384kbps file.

However when you play the file with either ffdshow or ac3filter, they say it's 6-channel (and yep, seems to have audio on all 6 channels too) ..

Is there a tool to edit the AC3 header without re-encoding the offending file?

[setarip_old]

Hi!

I don't know whether it will "do the trick" for you but, you might try "AC3Fix"...

[Barleyman]

Doesn't do anything about the headers.

In the end I simply decided to brute force it by using AC3 Filter to force output stream as 5.1 to make on-the-fly "conversion".

[tebasuna51]

Try with DelayCut and put the log

[SeeMoreDigital]

I have an AC3 file that the mediainfo, eac3to and others insist is a stereo 384kbps file.

However when you play the file with either ffdshow or ac3filter, they say it's 6-channel (and yep, seems to have audio on all 6 channels too) .. Does it run at 44.1Khz by any chance?

[Barleyman]

Does it run at 44.1Khz by any chance?

48kHz actually. And to make things better the stream changes to stereo a few times in the middle for 1 frame or so.

But like I said, I worked around it by setting ac3filter muxer to output 5.1 stream.

AFAIK there are no general purpose utilities to manipulate AC3 headers. I found one that lets you set EX flag but that's all.

[tebasuna51]

Capturing TV you can have a mix of stereo and 5.1 ac3 frames (commercials-movies).
You can't edit the headers because the frames are real stereo and real 5.1, change the headers produce a more severe error.

You need cut the not dominant frames. Is not simple but you can use DelayCut to do the job.

[Barleyman]

Capturing TV you can have a mix of stereo and 5.1 ac3 frames (commercials-movies).
You can't edit the headers because the frames are real stereo and real 5.1, change the headers produce a more severe error.

You need cut the not dominant frames. Is not simple but you can use DelayCut to do the job.

The problem is that the main header says it's 48kHz stereo file and that's that. 99.5% of the stream is 5.1, thought.

[tebasuna51]

The ac3 stream don't have main header, each frame have a header you must delete the first frames.

Use DelayCut and put the log (3th time).

[Barleyman]

The ac3 stream don't have main header, each frame have a header you must delete the first frames.

Use DelayCut and put the log (3th time).

You can repeat yourself as many times as you want, I already resolved the issue in 3rd post.

[Barleyman]

For what it's worth, I do believe the problem here was that the 1st frame of the AC3 stream was in stereo. Since all the codecs and most of the tools just check the first frame they freak out as 5.1 stream was expected. I was actually transcoding this to WMA 5.1 and the conversion tool quits with non-informative numeric error code. Also it was confusing when you checked the stream yourself as ffdshow said it's 5.1 because it shows real-time info.

Cutting out the stereo frames in the beginning would most likely have worked just fine but it was easier to make ac3filter to mix those few stereo frames to 5.1 instead. Plus no issues with audio synch this way.

[nautilus7]

You can repeat yourself as many times as you want, I already resolved the issue in 3rd post.This is the way you thank people trying to help?

[Hardcore Legend]

Well, since I'm having the same problem and choose not to be a jerk about it, here is the log I get:


[Input info]
Bitrate=384
Actual rate=384.000000
Sampling Frec=48000
TotalFrames=23926
Bytesperframe=1536.0000
Filesize=36750336
FrameDuration= 32.0000
Framespersecond= 31.2500
Duration=00:12:45.632
Channels mode=2/0: L+R
LFE=LFE: Not present
[Target info]
StartFrame=0
EndFrame=23925
NotFixedDelay= 0.0000
Duration=00:12:45.632
====== PROCESSING LOG ======================
Time 00:00:00.000; Frame#= 1. Some basic parameters changed between Frame #6 and this frame
Time 00:00:00.160; Frame#= 6. Some basic parameters changed between Frame #1 and this frame
Number of written frames = 23926
Number of Errors= 2


Now I know that the audio is actually 6ch (or 5.1), except for these stray, it appears 5 or 6 frames that make the file register as 2.0 Stereo.

As you told the person above, they need to cut these frames out. How do I go about doing that?

[Hardcore Legend]

By re-reading the thread, I think I figured it out.

I discovered the change was at frame 6, so I clipped the first 6 frames of the AC3. I then remuxed the m2v and the AC3, and with VideoReDo I adjusted the audio the difference of the lengths of my original file and the clipped file (160 ms).

This came out pretty close to the original. Close enough that I think I'm losing my mind thinking there is any difference in timing. :devil:

:thanks:to all those who helped in this thread. Now I can go back and correctly fix 900 HD recordings. Ha!

[jeffnoone]

Great thread, as I also have this problem. AC3Delay indicated problem at Frame #19 in the first of five clips - frame rate is 31.25 per sec
So I have a problem after about 0.61 sec into AC3 (19/31.25) - correct?

This a h264 HDTV .ts cap with AC35.1 sound

eac3to indicates the delay to be -752 msec: so minus means audio starts BEFORE the video - correct?

So that means the audio error is before the video even gets going - correct?

THis file is one of five (making up making up one of my favourite movies) - each of the five seems to have some error in the AC3 stream with each being reported as AC2.0 when the majority of the audio stream is 5.1

Now my my second question: if I join all five files together directly (leaving the faulty frames in place), then correct the start of the movie only - will this larger file play properly in 5.1 with players such as Zoom/AC3, or more inportantly if I stream to a PS3. I intend to join with eac3to which will fix delay automatically in two runs - correct?

So do I need to take out all faulty audio frames?

help appreciated

Thanks
Jeff

[tebasuna51]

... AC3Delay indicated problem at Frame #19 in the first of five clips - frame rate is 31.25 per sec
So I have a problem after about 0.61 sec into AC3 (19/31.25) - correct?
I don't know AC3Delay, I use DelayCut.
If ac3 is 48 KHz each frame is 32 ms. 19 frames -> 608 ms

eac3to indicates the delay to be -752 msec: so minus means audio starts BEFORE the video - correct?

So that means the audio error is before the video even gets going - correct?
Yep, you can use DelayCut to delete the first 23 or 24 frames (752/32 = 23.5). If you want join this part with other maybe you need adjust (adding ending silence with DelayCut also) the audio and video length.

Now my my second question: if I join all five files together directly (leaving the faulty frames in place),
Bad idea. Repeat the procedure with the five files.

... then correct the start of the movie only - will this larger file play properly in 5.1 with players such as Zoom/AC3, or more inportantly if I stream to a PS3. I intend to join with eac3to which will fix delay automatically in two runs - correct?
I don't know. Maybe. Eac3to can reject improper ac3 streams.
So do I need to take out all faulty audio frames?
Always recommended.