avi audio sync problem.

[Corpsecreate]

First off, I have read the stickied thread, and have tried some of the options there with no success. I will do my best to explain the problem I am having.

I have downloaded an episode of the TV series "24". Specifically, it is the 2nd episode of season 4 at a 1280x720 resolution. It is the only high definition version of this episode so finding an alternative download is not an option. This tv show was filmed at 23.976 fps but for it to be shown on NTSC TV, it had to be telecined to 29.970 fps and the encode of my file is 29.970 fps. I suspect this is where the cause of the problem lies.

Mediainfo copy/paste:

Video
ID : 0
Format : MPEG-4 Visual
Format profile : Simple@L3
Format settings, BVOP : No
Format settings, QPel : No
Format settings, GMC : No warppoints
Format settings, Matrix : Default (MPEG)
Codec ID : XVID
Codec ID/Hint : XviD
Duration : 42mn 53s
Bit rate : 4 296 Kbps
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate : 29.970 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Compression mode : Lossy
Bits/(Pixel*Frame) : 0.156
Stream size : 1.29 GiB (90%)
Writing library : XviD 1.0.2 (UTC 2004-08-29)

Audio
ID : 1
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Codec ID : 2000
Duration : 42mn 52s
Bit rate mode : Constant
Bit rate : 448 Kbps
Channel(s) : 6 channels
Channel positions : Front: L C R, Side: L R, LFE
Sampling rate : 48.0 KHz
Bit depth : 16 bits
Compression mode : Lossy
Delay relative to video : 31ms
Stream size : 137 MiB (9%)
Alignment : Split accross interleaves
Interleave, duration : 33 ms (1.00 video frame)
Interleave, preload duration : 500 ms

The problem I have is that the audio is synced up with the video at the start, but as time progresses, the audio gets further ahead of the video. The length of the video is 77,135 frames or 42 Minutes and 53.73 Seconds. The length of the audio is 42 Minutes and 52.67 Seconds. So the audio is 1.06 Seconds shorter than the video. With each attempt at a fix, I have tried watching the video in 4 different players (VLC, MPC, WMP, Daum Potplayer) and they all have the same problem.

My first attempt to fix this, was to simply shift the audio behind by some set amount of time. I didnt expect this to work for obvious reasons, shifting it back would just cause it to be out of sync at the beginning and would resync toward the end. I tried it anyway, and as expected, it didnt work.

My second attempt was to alter the framerate of the video so that the video would be equal to the duration of the audio. With a little bit of math I calculated the required fps to 29.982. The accuracy of my calculation was confirmed when I opened the file in virtualdub and used the "change so video and audio durations match" option. So I edited the video to 29.982 fps (with 3 seperate programs) and tried again. This time, the video was desynced at the start of the video and then resynced up toward the end. I don't understand why this still did not fix the problem.

My third attempt was to rip out the audio on its own and slow down the audio so that it matches the duration of the video. This is basically the same as my second attempt. So I changed the audio to .wav, opened it up in Audacity and used the change tempo function to match the duration of the video. I then remuxed them together and the result was exactly the same as my second attempt. It was out of sync at the start and was in sync at the end.

So, I'm out of ideas. What else can I do?

[locotus]

I guess you're somehow confused, 23.976 and 29.970 are both used in ntsc videos,
so you are not supose to change anything to view your file.

[Corpsecreate]

As far as I understand. 23.976 is used for NTSC Film and 29.970 is used for NTSC TV. For 23.976 fps film to be shown on 60hz tv, the frames must be stretched to fit a multiple of 60 (30). This process is known as Telecine or 3:2 pulldown. Right or wrong, my problem still remains

[hech54]

Just buy the DVD and stop pirating.....problem solved.

[Corpsecreate]

I would gladly buy it (like I have bought Season 7 and 8) if they would release it in HD. This is the only version that exists in HD atm so I have no choice.

So I just found out the real cause of the problem but i'm not sure of the best way to fix it. It seems that the audio desynchs occur after where tv ads have been cut. So it looks like that when each piece was joined together, the timing of the audio did not match the video. Any any idea on the best way to fix this?

[davexnet]

Yes - you should split the file there, fix the rest of it, and them join it back together.

[Baldrick]

WAIT for the blu-ray release of 24 season 4 or until it's aired on a hd channel and record. Resyncing warez material is not worth it.