How do I timestretch 5.1 AC3

[jodal]

Hello!
I live in a PAL country (Sweden) where the standard video framerate is 25 fps.
I have an mkv HD movie with framerate 23.97 fps and english 5.1 DTS audio in sync with video. I also have a PAL DVD of the same movie from which I have extracted the swedish 5.1 ac3 audiotrack and since I have children who does not yet read I would like to add this ac3 track to my mkv. With mkvmerge I can easily do this BUT the swedish audiotrack (as well as the corresponding video) is shorter than the english by a factor of 23.97/25 (i.e. the swedish movie has just been upspeeded by this factor compared to the original). What I would like to do is therefore the opposite operation, timestretching the swedish ac3 track with a factor 25/23.97 (or 25025/24000 to be exact). There is an option for timestretching in mkvmerge but the result is an audiotrack that stutters a lot an is unusable for a pleasant viewing experience. I tried converting the 5.1 ac3 track to a stereo wav file, stretch that and convert back to 2 chanel ac3 and that works fine but the I loose the 5.1 sound.
So is it possible to (rather simple) timestretch an 5.1 ac3 file?

[poisondeathray]

You can use besweet, eac3to, or audacity to change the fps. Besweet even has presets PAL to NTSC 25=>23.976 etc...

eac3to is very easy to use if you use commandline

eac3to input.ac3 output.ac3 -slowdown

[jman98]

If your children are small, I doubt that they will notice or care that your audio is "only" 2 channel AC3.

[jodal]

Thank you very much for your help poisondeathray. I sfirst gave besweet a try but it woudnr run due to the lack of some dll which I guess is related to me running win7 x64. Next in line was eac3to and newbie as I am I couldn´t find anywhere to write the commands (the cmd window showed a lot of activity and thn disappeared each time I ran the eac3to.exe file) so I downloaded a GUI and voilá - it performed exactly what I wanted (and the commandline was exactly as you wrote). It also seemed to remove some dialogue normalization although I did not ask for that but I havent been able to run in in a 5.1 sustem yet to hear if that is something to bother with.
Anyway, you gave me a quick and very helpful answer that solved my problem so thanks a lot again.

best regards
Jodal

[jodal]

jman98: I do not want to be rude but it should be obvious that I´m not satisfied with 2 channel ac3 since (as it says in the post) I already done that and yet post this question on the forum. Its much nicer with replies that actually tries to answer the question.

thanks anyway for your input
best regards
Jodal

[poisondeathray]

It also seemed to remove some dialogue normalization although I did not ask for that but I havent been able to run in in a 5.1 sustem yet to hear if that is something to bother with.

If you wanted to keep it, add this to commandline

-keepDialnorm

Here are some of the eac3to commands if you are interested
http://en.wikibooks.org/wiki/Eac3to/How_to_Use

[Cornucopia]

I'm glad you got what you wanted. But for the sake of other users who might want to try a similar thing, there is one BIG thing to understand about this process:

There can be a good chance that, even if the running time seems equivalent, the various transfers could come from masters different enough in their editing that there will be major mis-sync. Sometimes it gets to the point where you'd have to "re-edit" the audio from scratch.

In my opinion, you lucked out this time.

Scott

[jodal]

Thanks again for useful info and I will definately check out the wiki site since I might be doing something similar in the future (its always nice to learn new things).
Scott, I am aware that it might notalways work but I have now done two more movies which has worked out as expected (I havent wathed them all through but checked variuos points in time throughout the movies and they are all in sync so far. It might not work for every movie but I am glad I got these to work and as said before, its nice to learn new techniques since I like to fiddle with audio/video.

best regards
Jodal