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Topic: 2-Channel MP2 or AC3 (Read 4622 times) previous topic - next topic
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2-Channel MP2 or AC3

Hi.  I'm sorta new to all this.  I have a PAL concert recording from a European satellite broadcast.  In addition to struggling to convert it to NTSC as best as possible, I would prefer to only have one soundtrack.  It has a 2-channel MP2 audio track at 256kbps and a 2-channel AC3 audio track at 384kbps.  Both are at 48kHz/16bit.  I am assuming that the 2-channel AC3 soundtrack would be preferable.  Is this correct?  TIA.

2-Channel MP2 or AC3

Reply #1
You might already know how audio transcoding is frowned upon. And this applies equally well, perhaps more to video. Apart from MPEG compression, the framerate conversion process is very lossy, so you best keep the video as 25/50 fps. The PAL/NTSC standards are yesterday. Today all devices are computers and it's only the matter of synchronizing the display and video properly.

About the audio. You can't really tell that it's source resolution was 16-bit. The bit count could be more or less, and can only be determined by closely examining the waveform and only if there is no noise (practically impossible). Both audio tracks should be compared for sound quality or, if you don't hear any difference, at least graphically analyzed. It is possible that the studio/transmitter created one stream from an inferior source, such as the other stream. Both AC-3 and MPEG Layer-2 formats should be transparent at these bitrates, but quality of the encoding process (e.g, LAME vs Xing) and the source of each one is unknown at this point.

2-Channel MP2 or AC3

Reply #2
You might already know how audio transcoding is frowned upon. And this applies equally well, perhaps more to video. Apart from MPEG compression, the framerate conversion process is very lossy, so you best keep the video as 25/50 fps. The PAL/NTSC standards are yesterday. Today all devices are computers and it's only the matter of synchronizing the display and video properly.
I'm not sure what you are saying exactly.  I know that when you change the framerate, the audio has to somehow still be synced which, from my limited understanding, is problematic.  I want to burn this to DVD for playback on a NTSC-only player.  Will it be able to play the NTSC video if it is at the same 25 fps framerate as the PAL?  I thought I had to also convert it from 25 to 29.97.  The software solutions I have at my disposal (re: cheap) are not doing the PAL to NTSC video conversion so well, but the audio seems to be synced.  The original PAL video looks great (on a computer screen).  From my reading, I think that the best way to do this is to strip the audio content, convert the video separately, then sync the audio track back to the video.  I really do not want to over-think this.  I would just like a nice copy to play on my DVD player.  If there are any resources you can recommend, please do.  Thanks.


About the audio. You can't really tell that it's source resolution was 16-bit. The bit count could be more or less, and can only be determined by closely examining the waveform and only if there is no noise (practically impossible). Both audio tracks should be compared for sound quality or, if you don't hear any difference, at least graphically analyzed. It is possible that the studio/transmitter created one stream from an inferior source, such as the other stream. Both AC-3 and MPEG Layer-2 formats should be transparent at these bitrates, but quality of the encoding process (e.g, LAME vs Xing) and the source of each one is unknown at this point.
The AC3 audio sounds best, I suppose.  Of course, that is on my computer.  I guess what I was wondering was if that was just an illusion created by the AC3 encoding.  I think that the MP2 track is included because that is a requirement in Europe.  I don't want to over-analyze this (it's just a concert).  I am just going to assume the AC3 track is probably best and move on.  The video conversion is what I really need to tackle.

Thanks, again. 

2-Channel MP2 or AC3

Reply #3
If you're converting from 50fps video (European) to 59.94fps video (American) the audio does not change. You are editing only the video stream: inserting extra frames. Audio continues to run at the same speed and does not need to be touched. Regular video shows up interlaced on a computer screen (without further processing).

However, if you're converting from 50fps film video, which has been sped up before displaying in PAL, to NTSC format, audio should be resampled. It's because you would like to correct this speedup and treat the video at its true 24fps rate. Film video shows up progressive (normal) on a computer screen.

The professionals at Doom9 will usually be of great help with these questions. Just make sure you do some own research before posting there.

 
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