MPEG-2 remux

[nicolasete33]

Hi,

I have a MPEG-2 PS file with two audios and I need to replace the content of one of them with another audio file (same duration and format but different content).

I can not modify the size of the original file for compatibility reasons and I want to know if there is any tool that could just do this replacement of the content of one stream PID content without demux and remux the whole file.

Regards.

[Chris K]

I don't think it can be done. Same duration and same format doesn't mean explicitly the same file size.
You can only overwrite the audio packets in the PS stream with the same number of bytes. I don't think there's a tool that does this cause it would be exceptional if it worked. Only way is demux/remux.

[guns1inger]

Demux the tracks (video + two audio). Look at the stats of the audio you are replacing. Encode your new audio to match. Same bitrate and running time should give same file size. Remux with new audio tracks.

[Chris K]

Demux the tracks (video + two audio). Look at the stats of the audio you are replacing. Encode your new audio to match. Same bitrate and running time should give same file size. Remux with new audio tracks.

You're right. Tried it with AC3 from two different sources. Excactly the same # of bytes. Probably was thinking of VBR for audio.
However what nicolasete33 asks is to do it without remuxing. With the same file size it would be remuxed just as useful as the original, I think.

[nicolasete33]

You are right Chris. I can not demux/remux.

Audio tracks are Musicam 256 Kbps, which is a deterministic format regarding the size of the "packets". That is why I thought about just "replacing" old packets with new packets.

Thanks for your help.

[Cornucopia]

Musicam is just the old name for MPEG1,Layer1 audio streams (prior to being folded into the MPEG clan).

Encoding your new audio (edited to EXACT same length) to MPEG1, Layer1 @ 256kbps CBR (using something like TMPGEnc) should give you a "compatible" file of very close to the same size.

You're going to have to demux and remux, unless you want the drudgery of hexediting a 100's of MByte file.

Why do you think that demuxing/remuxing will ruin your compatibility?
That's what apps like DVDRemakePro successfully do all the time (compatibly replace items).

Scott

[SatStorm]

Musicam is the mp2 audio files, used on DVB transmissions and on the European DVDs.
It is MPEG-1 Audio Layer II, and it is the closest audio codec to mp3 (actually the core for mp3). Mp2 offers slighty better audio on higher bitrates (192kb/s or more) while Mp3 offers better audio on 128kb/s.

[Cornucopia]

My mistake. SatStorm is correct. I was thinking of DCC/PASC for MP1.

The rest of what I said still holds.

Scott