mpa from DVB transmission problem

[SatStorm]

Okey, I grabbed that german channel from satellite, so I have a mpeg 2 file, muxed as DVD. I grabbed the stream, I didn't cap (using nokia 9600, dvb2000 firmware and DVBrecorder 1.19d if someone interest to know how).
Now, this german DVB channel (3Sat) has a "problem" (common with german DVB channels): It change the audio from mono to stereo and vice versa from one show to other.
So, I end up with a file, that starts with the sound OK, then the sound pause for half a second (the video continues as is...) and then returns speeded up. The result is like hearing Snumfs talking!
Obviously, there are some flags missing in the stream or the flags changed during the transmission and the grabbing program simply forgot to add the new ones during multiplexing...

DVD2avi seems to correct those missing flags, if I load this mpeg 2 file to it, and save a project, but after the start point of this audio problem. Using "decode" and "auto selection", I end up with an mpa file which plays okey, so I believe that dvd2avi somehow set this "flag" or watever to the audio.

Unfortunatelly, now I have a file that I didn't do this trick, because I thought that the audio was okey. And because it was a 3 part mpeg 2 recording (I use to set the program automaticly split the transmission to files, about 20min each), I did the fault and join them with mpeg2vcr alltogether.
Well, with this new file, the "DVD2avi trick" doesn't work. Seems like mpeg2vcr set some kinds of flags during the joing, and I can't reverse that.

So, my question is: Is there an audio patcher for those mpa's? Something like "avifrate" for avi's? I mean, I can seperate the problematic audio part with dvd2avi (or other programs) in an mpa or mp2 form, so is there any way to patch the audio to return to it's normal speed?
There is no audio info missing, there is no encoding proccess took place. It is simply a mpa (or mp2 if you like) from a DVB channel, which somehow has a wrong tempo!
Just to add that loading the file to audio programs like soundforge and try to compress/expend the time by changing the tempo ain't working (which is natural, this is not the case here....)

I need help on this!
Thanks in advance!

[ronnylov]

You would need something that restores the missing header that contains info about the mp2 file. The header is probably in the beginning of the file so maybe if you could cut out the stereo and mono parts and replace the headers. Maybe you can examine another file that is correct and try to fix it. I don't exactly know how...

There are gurus on the hydrogenaudio forum that may help you.
http://www.hydrogenaudio.org

Please report back if you find the solution because I also see this sometimes on my DVB-C captures but luckily it has been fixed mostly during the demuxing with pvastrumento (the bad audio part in the beginning was simply cut off, both video and audio, before the movie started). Perhaps you can try to demux your mpg with pvastruento? Try both 2.0.30 and the 2.1 pretest versions because they behave differently. I've had most success with version 2.0.30.

EDIT: Maybe there is a way to fix it with BeSplit: http://besplit.doom9.org/

[SatStorm]

OK, I didn't find any direct digital solution, but I found a solution anyway...
First of all, I used Soundforge (an ancient version I own, I thing 4.5g or something).

First of all, why that happened: The transmission was first stereo (2 channels) and for bitrate reasons change it to mono (1 channel). But because the multiplexxing was realtime, the program added once in the start of the file the audio info of the channel, and keep multiplexxing whatever coming from satellite.

The first info was 48000Khz 192Kb/s. That changed to 24000Khz 192Kb/s (half bandwith). But the headers keep pointing 48000Khz, so any player / decoder keep playing the 24000Khz as 48000Khz. This is double speed ofcourse ("Snumfs talking" effect...)

The solution was easy: I demux the mpeg 2 file to m2v and mp2. I loaded mp2 to Soundforge. Soundforge turn it to wave. I marked the bad audio part, copy it and paste it to a new window. I also copy the good audio part and paste it in another window. I returned to the bad audio part and I changed the samplerate from 48000Khz to 24000Khz (manual). I Only applied Samplerate, I didn't convert the audio. That is important!. After this, the bad audio part played perfect speed.
Now, I converted the samplerate from 24000 to 48000??z but this time I also choose to convert the audio. I join the bad part of audio with the good part of the audio and I save the wav file to HD.
I encoded it to mp2 using tooLAME and I multiplexx it with the m2v. Finally, I have perfect Lipsynch video / audio and no more Mickey Mouse talking!

Thanks all for your help!

[ronnylov]

I noticed something interesting when I tried pvastrumento 2.1pre9 version. I started to record before the movie started and the aspect ratio was set to 4:3 but then the movie started and aspect ratio changed to 16:9 and after the movie it changed back to 4:3. PVAStrumento detected it and splitted it into three parts, before movie, movie and after movie! This was perfect, I did not have to edit anything manually.

I had a similar experience with pvastrumento (don't remember the version). The audio changed from stereo to mono and a lower bitrate when the movie started. PVAStrumento just returned the movie and the other parts were discarded. So sometimes it is a good thing that parameters changes because it makes editing much easier if the demuxer can split it autmatically at parameter change (it usually means that a new tv program has started).

[SatStorm]

This is depending your source!
You see,if you use nokia 9600 and dvbrecorder as I do, you can't use pvastrumento (any version) for this.

This tool (pvastrumento 2.1pre9) is good for proccessing dvb captured from PCI cards, basic in a pva format.

My system grabbs, remove the pading and remultiplexx video/audio realtime on an mpeg 2 file, ready as it to be loaded to any authoring program (if the resolusion is 720 x 576, 704 x 576, 352 x 576 or 352 x 288 - Yes, there are DVB channels in Europe using this framesize....)

In short terms, in my case, pvastrumento is useless...