Sign in with
Sign up | Sign in
Your question

AV Sync problem when resampling AVI

Last response: in Graphics & Displays
Share
Anonymous
April 11, 2005 6:12:59 AM

Archived from groups: rec.video.desktop (More info?)

Using transcode/mplex to convert AVI video files to MPEG4 for making a
DVD usually works very nicely, but I have a few AVI videos with the
audio at 14400 mhz that are giving me problems. For these files I
enable the -J resample option in transcode to convert the audio to 48000
mhz. The videos are approximately 350 MB. This resampling proceeds
with out any error messages, but the resulting MPG file is less than
perfect.....

At the beginning of the newly made MPEG4 video the audio and video are
in sync. As the video plays the AV sync gradually drifts apart. By the
end of the video, the AV sync is several seconds off. If I use
transcode without the -J resample option, the AV sync is fine through
out the video, but then the audio is still at 14400 mhz and it will not
work with dvdauthor.
What can I do to keep the AV in sync at 48000 mhz??

John
Anonymous
April 11, 2005 7:24:58 AM

Archived from groups: rec.video.desktop (More info?)

John Scudder wrote:
> Using transcode/mplex to convert AVI video files to MPEG4 for making a
> DVD usually works very nicely, but I have a few AVI videos with the
> audio at 14400 mhz that are giving me problems. For these files I
> enable the -J resample option in transcode to convert the audio to 48000
> mhz. The videos are approximately 350 MB. This resampling proceeds
> with out any error messages, but the resulting MPG file is less than
> perfect.....
>
> At the beginning of the newly made MPEG4 video the audio and video are
> in sync. As the video plays the AV sync gradually drifts apart. By the
> end of the video, the AV sync is several seconds off. If I use
> transcode without the -J resample option, the AV sync is fine through
> out the video, but then the audio is still at 14400 mhz and it will not
> work with dvdauthor.
> What can I do to keep the AV in sync at 48000 mhz??
>
> John

Pardon my dyslexia, I meant '44100 hz' not '14400 mhz'

John
Anonymous
April 12, 2005 3:41:45 AM

Archived from groups: rec.video.desktop (More info?)

B. Peg wrote:
> This is what I have saved and written down on an AVI rip I did where the
> audio synch was off at the end. Maybe it'll help, maybe not. Anyhoo, here
> it is:
>
> One theory is if the sound card is not really at 44,100 Hz and is actually
> at 44,109, then the audio could be off several seconds at the end of the
> movie - sort of a compression or expansion of the audio file. This one
> might
> explain why a ripped movie is different when played on various players or
> computers.
>
> I did one tonight where the audio and video synch was off a few seconds on a
> DivX AVI movie rip I did to put it in my portable player. The thing was off
> a little at the beginning and a bunch at the end.
>
> A couple of pieces of software can help: VirtualDub and SoundForge
> (VirtualDub is free, other is trial I believe but I bought SF as I like it).
>
> Here is the outline as I wrote it down:
> Open the AVI file in VirtualDub and make note of the frame counter time
> (bottom of screen) for a sound near the beginning and one near the end. I
> used someone banging a hammer for one and shouting at the end.
>
> In VirtualDub, you can rip a WAV file out of the AVI file. Using
> SoundForge, load the large WAV file and scan to the two "approximate" times
> noted above and listen for the sounds you are using to mark the file (i.e.
> the hammer and shout noise in mine). Make an exact note of the "real
> occurring time" of the two noises at the bottom of the screen in SoundForge.
> Add or subtract the two times in SoundForge from the frame video times in
> VirtualDub. The object is to get the two times to agree with each other as
> close as you can.
>
> You can shift the WAV file time ahead or back using either a Insert Time at
> the beginning of the WAV file or subtract it to match the above video frame
> times. No doubt they "both" will not match doing so.
>
> Now come the little trick. You can use Resample in SoundForge and shift the
> audio (either compress or expand the length of the track). Open Resample
> (leave anti-alias off), check the box regarding "Sample Only" so you do not
> save it yet, and change the Sample Rate from 44,100 Hz to say 44,110 and see
> where the new audio times are in comparison to the frame times earlier done.
> You can increment or decrement the 44,100 number and watch the audio times
> change. The idea is to change it and get it to closely match the video
> frames. You cannot get it exact but close.
>
> Once done, set the Resample back to 44,100, uncheck the Sample only box, and
> save it. You can then set both the video and audio pulldowns in VirtualDub
> to Streaming and load the AVI file. Under the Audio select your new WAV,
> Press F7 (or Save AVI), and let it rip. It's pretty fast here (4-5
> minutes).
>
> However, now you have a DivX AVI with a WAV file and it's pretty large. Run
> it back through VirtualDub. Turn on Full Processing Mode in both Video and
> Audio pulldowns. Set the video Compression codecs for DivX; the audio
> Compression for LAME Mp3 (set to around 44,100 Hz, 128 Constant Bit Rate
> (CBR - not variable or average), Stereo. You can also alter the Video
> filter with a bit of Brightness and Contrast (mine always seems so dark in
> Windows Media Player). This run will take longer (30 mins) and the file
> will be much smaller.
>
> That's as much as I remember.....whew!
>
> Good luck.
>
> B~
>
>
Thanks for the suggestion. Since I am not using Windows I won't be
able to do exactly what you did using VirtualDub and Soundforge , but I
think I can pretty much follow the same steps using comparable Linux
programs.
!