Encoding multi-pass 1st pass doesn't work

[amirh1]

Hi,
I use VirtualDub 1.7.7 to encode a video using DivX 6.8.3 codec. I select "multipass, 1st pass" and leave the settings to default. However, no matter what bitrate I use, only the audio gets encoded, resulting in a small audio file. I'm pretty sure I have video encoding setup properly because if I change *only* the Rate Control to "1-pass" the video encodes fine.

I have this same result using different versions of virtualdub and different versions of DivX.

Please - any help would be greatly appreciated!!

Thanks,
Amir.

[Dark Shikari]

That's normal: it only saves the statsfile, not the output video, on the first pass.

Once the 1st pass is done, run the 2nd pass, and that will generate the final video file.

[amirh1]

Thanks Dark Shikari! What do I select for the 2nd pass? The Rate Control options only have "Multipass, Nth pass" and if I just try to re-encode using same settings the same output is generated. Sorry for the newbieness (I've never done multipass before)

That's normal: it only saves the statsfile, not the output video, on the first pass.

Once the 1st pass is done, run the 2nd pass, and that will generate the final video file.

[DigitAl56K]

You're doing it right:


Run the 1st pass
Run the nth pass at least once


Do this without changing the video or the settings between passes and simply overwrite the output file from the last pass with the new pass. Turn off audio encoding until the last pass if you're also doing that in VDub. The encoder also has a "Fast 1st pass" built in that is functionally the same as the regular first pass except that internally the encoder may tweak some of your settings behind the scenes to run the first pass in less time. As I recall, a fast 1st pass in balanced mode can take up to 35% less time and higher quality modes benefit even more.

[amirh1]

Thanks for the help - works great!

[DigitAl56K]

Good stuff,

If you haven't used VirtualDub much before also check out it's job manager and the ability to save tasks to the job queue instead of running them immediately via the Save dialog. This lets you queue up multiple passes and start them without having to manually return to the computer later to trigger the nth pass.

[amirh1]

Thanks DigitAl56K - that's a great tip I didn't think of! Yes, I kept coming back for the next pass (although I used xvid so that's only two passes it can do).

If I use filters, I assume I must re-run the 1st pass after every filter change. However, your tip applies to that too - I assume the batch jobs remember filter settings as well, so I could do batch [1st filter, 1st pass][1st filter, 2nd pass][2nd filter, 1st pass]... etc. This will really save me time!!

Good stuff,

If you haven't used VirtualDub much before also check out it's job manager and the ability to save tasks to the job queue instead of running them immediately via the Save dialog. This lets you queue up multiple passes and start them without having to manually return to the computer later to trigger the nth pass.

[Dark Shikari]

Thanks DigitAl56K - that's a great tip I didn't think of! Yes, I kept coming back for the next pass (although I used xvid so that's only two passes it can do). I'm pretty sure Xvid can do N passes too, however useless such a feature is.

[Blue_MiSfit]

If you're running a very slow script, it may be beneficial to encode to a lossless format first, and use that as a source for DivX encoding (since reading a lossless file can happen very quickly, as opposed to running the filter chain 2-3 times)

-MiSfit

[DigitAl56K]

If I use filters, I assume I must re-run the 1st pass after every filter change.

It is safest to, yes. I think certain types of filters (e.g. uniform level adjust) will not affect the relative texture/motion complexities too much, but making that assumption is a bit of a gamble.

However, your tip applies to that too - I assume the batch jobs remember filter settings as well, so I could do batch [1st filter, 1st pass][1st filter, 2nd pass][2nd filter, 1st pass]... etc. This will really save me time!!

Yes, you can actually save the jobs list from the management window and open it with notepad and see exactly what's in there. It's a text file filled with sylia script describing all of the operations virtualdub has to perform for each job.

I don't quite understand why you would want to change filters and then encode the entire file over again. Why not set up your filters properly before encoding the multipass? If you want to do a quick quality check mark an appropriate selection on the timeline and export using 1-pass quality based mode to see what it looks like.

[amirh1]

I don't quite understand why you would want to change filters and then encode the entire file over again. Why not set up your filters properly before encoding the multipass? If you want to do a quick quality check mark an appropriate selection on the timeline and export using 1-pass quality based mode to see what it looks like.

I mainly just add the "2:1 reduction" for sending via email - the rest I leave unchanged. So for every clip, I have the standard set of filters and then for some of them I add the reduction filter, thereby requiring doing the 1st pass over again.

[Brother John]

I'm pretty sure Xvid can do N passes too, however useless such a feature is.
Theoretically it can, but updating the stats file in 2nd pass isn’t implemented. So max 2 passes for Xvid. Not that it’d be a disadvantage. :)