girotour
5th January 2003, 01:36
Hi all.
I'm trying to undestand how exactly audio/video synchronization works with DVD2SVCD.
I'm making a lot of tests, but I have some doubts that I'm not able to solve.
Here they are.
Let's start from the following rip:
0x20 - Subtitle - English / LBA: 21733 / PTS: 00:00:51.167 / Delay: 50800ms
0x80 - Audio - AC3 / 6ch / 48kHz / DRC / English / LBA: 115 / PTS: 00:00:00.287 / Delay: -80ms
0xE0 - Video - MPEG-2 / 720x576 (PAL) / 16:9 / Letterboxed / LBA: 1 / PTS: 00:00:00.367 / Delay: 0ms
Doubt #1: audio delay.
In the example, the audio track has a delay of -80ms.
So, if I understand well:
1) Audio track starts
2) After 80ms video track starts
Looking at the DVD2SVCD log, when the program converts the audio track to mp2 format, it executes:
"C:\Program Files\DVD2SVCD\BeSweet\BeSweet.exe" ... -ota( -d -80 ) ...
This way it runs BeSweet telling it to add -80ms of delay to the output file.
But: how can a negative delay be added?
I understand how to add a positive delay; probably you simply add some silence at the begining of the file. But how can you add a negative delay?
I've just two hypothesis:
1) First 80ms will be simply removed
2) Delay time is just a parameter which will be inserted into mp2 file and will be used by bbMPEG when it will mux audio and video tracks
Doubt #2: delay when muxing audio and video.
In bbMPEG we can find three parameters: "Video stream startup delay", "Audio 1 stream startup delay" and "Audio 2 stream startup delay".
Trying to understand which role they play, I made the following tests:
1) I converted a DVD chapter manteining the parameter default values (180, 180, 180)
2) I converted the same chapter using big values (10000, 10000, 10000)
The result was.. exactly the same!
Also in this case I've an hypothesis. These parameters are not delay values but simply reference times.
In the first case bbMPEG started audio track after 100ms (180 - 80) and video track after 180ms (180 - 0).
In the second case bbMPEG started audio track after 9920ms (10000 - 80) and video track after 10000ms (10000 - 0).
Reference times are different, but tracks offset is the same. So, the result is the same.
Is it correct?
Doubt #3: Movie offset seconds
Ok I understand that, generally speaking, "it can solve desync on dvd players", but why? What's wrong with the default bbMPEG output when I decide to set that parameter to 0.
I hope that some guru around will be able to show me the light. ;)
Thx in advance.
I'm trying to undestand how exactly audio/video synchronization works with DVD2SVCD.
I'm making a lot of tests, but I have some doubts that I'm not able to solve.
Here they are.
Let's start from the following rip:
0x20 - Subtitle - English / LBA: 21733 / PTS: 00:00:51.167 / Delay: 50800ms
0x80 - Audio - AC3 / 6ch / 48kHz / DRC / English / LBA: 115 / PTS: 00:00:00.287 / Delay: -80ms
0xE0 - Video - MPEG-2 / 720x576 (PAL) / 16:9 / Letterboxed / LBA: 1 / PTS: 00:00:00.367 / Delay: 0ms
Doubt #1: audio delay.
In the example, the audio track has a delay of -80ms.
So, if I understand well:
1) Audio track starts
2) After 80ms video track starts
Looking at the DVD2SVCD log, when the program converts the audio track to mp2 format, it executes:
"C:\Program Files\DVD2SVCD\BeSweet\BeSweet.exe" ... -ota( -d -80 ) ...
This way it runs BeSweet telling it to add -80ms of delay to the output file.
But: how can a negative delay be added?
I understand how to add a positive delay; probably you simply add some silence at the begining of the file. But how can you add a negative delay?
I've just two hypothesis:
1) First 80ms will be simply removed
2) Delay time is just a parameter which will be inserted into mp2 file and will be used by bbMPEG when it will mux audio and video tracks
Doubt #2: delay when muxing audio and video.
In bbMPEG we can find three parameters: "Video stream startup delay", "Audio 1 stream startup delay" and "Audio 2 stream startup delay".
Trying to understand which role they play, I made the following tests:
1) I converted a DVD chapter manteining the parameter default values (180, 180, 180)
2) I converted the same chapter using big values (10000, 10000, 10000)
The result was.. exactly the same!
Also in this case I've an hypothesis. These parameters are not delay values but simply reference times.
In the first case bbMPEG started audio track after 100ms (180 - 80) and video track after 180ms (180 - 0).
In the second case bbMPEG started audio track after 9920ms (10000 - 80) and video track after 10000ms (10000 - 0).
Reference times are different, but tracks offset is the same. So, the result is the same.
Is it correct?
Doubt #3: Movie offset seconds
Ok I understand that, generally speaking, "it can solve desync on dvd players", but why? What's wrong with the default bbMPEG output when I decide to set that parameter to 0.
I hope that some guru around will be able to show me the light. ;)
Thx in advance.