ffmpeggui experimenting LPCM to AC3

[hech54]

OK...here is the info I have:

Ripped a test chapter with DVDDecrypter, demuxed video and audio.
Audio is LPCM 2 channel 48khz - 16bit Delay -270ms.
Video is MPEG2 - 720x576(PAL) of course.
Loaded the LPCM into ffmpeggui and encoded at AC3 - 224 - 48000 2 channel
Ffmpeggui reads the file as PCM 48000rate 2 Channels bitrate 327sec
Remuxed with TMPGEnc Plus
Played the result in PowerDVD but sound it a tiny bit out of sync....but
MUCH better than my previous attempts(like at AC3 192). Most people
probably would not notice the sync issue but it is a guitar piece and
I am also a guitar player so I know it is a bit out of sync.

Is my AC3 bitrate wrong?
When I display the file info in PowerDVD the Video: MPEG-2 Mbps is not constant.

I'm new at this sort of stuff as you can see. Any advise would
be appreciated. I'm just experimenting with converting LPCM to AC3
in case I need to do this in the future....and since I have no fancy
entertainment system....my normal listening is through the TV speakers and
usually want video quality over audio quality.


I also tried Jimmalenkos Goldwave trick posted here:
https://forum.videohelp.com/viewtopic.php?p=1424216#1424216
but I obviously did something wrong since the result was WAY off. I couldn't use virtualdub to give me the exact run time so I loaded
the LPCM file in Prassi Ones as if I was going to burn an audio CD...WRONG!!

Anyway...any light you can shed?....
Thanks again
hech54

[guns1inger]

I use either 192 or 224 kbps for 2 channel AC3 depending on the quality of the source. If the video is VBR encoded (Variable BitRate) then the bitrate will fluctuate during playback. Even CBR encoding isn't truely constant.

There are tools that can change the delay in an AC3 file. Perhaps you need to experiment with one of those to correct the sync. issue. I have used AC3 Delay Corrector in the past and it seems to work OK.

[jimmalenko]

IMHO it should have absolutely nothing to do with the bitrate you select.

Audio is LPCM 2 channel 48khz - 16bit Delay -270ms

That's the key right there - IIRC a negative Delay value means that the audio "leads" the video. I'm guessing your audio is a fraction late in your MPEG ?

Besweet (through BeLight or the BeSweet GUI) can add this delay for you. ffmpeg (the commandline version) probably can too with the right commands.

An easy way to check if this is all it is would be to load your multiplexed out-of-sync video into virtualdubmpeg2 or virtualdubmod and play around with the audio skew property (under Interleaving). If you set this to -270 and then play the video, it should be right.

[hech54]

The DVD I took this from also has 5.1 AC3 as well. Is it possible to simply copy the delay from that audio and create that same delay in the new one?

[hech54]

IMHO it should have absolutely nothing to do with the bitrate you select.

Audio is LPCM 2 channel 48khz - 16bit Delay -270ms

That's the key right there - IIRC a negative Delay value means that the audio "leads" the video. I'm guessing your audio is a fraction late in your MPEG ?

Besweet (through BeLight or the BeSweet GUI) can add this delay for you. ffmpeg (the commandline version) probably can too with the right commands.

An easy way to check if this is all it is would be to load your multiplexed out-of-sync video into virtualdubmpeg2 or virtualdubmod and play around with the audio skew property (under Interleaving). If you set this to -270 and then play the video, it should be right.

Thank You...I'll try virtualdub - MPEG2 first.
I can't really tell what is lagging behind....the video or the audio....it is that close....but something is wrong. I'll play a bit.

[hech54]

Well....in virtualdubmpeg the audio is MUCH worse and nothing I do seems to change it.
I've never had much luck with virtualdub.

[wulf109]

Ripping one chapter could be the problem. Rip the entire "movie". Use PGC Demux to separate the LPCM stream. Only the first vob in a VTS contains the header information. I use ffmpegui often to convert PCM to ac3 and have never expierenced a degraded sound or audio synch problem.

[hech54]

That was my thought as well but I've just been experimenting. I've always taken the whole video with DVDDecrypter, demuxed and set File Splitting NONE in the past to make sure it all comes out right. As it sits right now.....in some programs I'm reading several lenghts of video and audio.
5:26
5:55.38
355.58 sec
3:20
I think I'm going to need to "experiment" with the whole concert instead of one chapter/song.