VFR encoding, x264, and you.

[Dark Shikari]

Buried in a recent commit message is a feature that may make life a bit easier for a lot of fansubbers.

Anyone with any experience encoding VFR fansubs will probably have noticed that --bitrate doesn't work as expected. This is, of course, because you're feeding constant framerate data to x264 and so x264 thinks the video is longer (or shorter) than it actually is. Prior to that commit, there was no other option: x264 simply didn't do VFR calculations inside ratecontrol.

Furthermore, VBV-maxrate didn't work correctly either; an encoder trying to limit the local bitrate of the video to play back better on low-end systems would not get what he expected either. Areas with high framerate would get more bitrate than he wanted.

Now x264 supports variable-framerate input, ratecontrol, and output, eliminating all of the above problems. Here's two different ways to do it:

1. x264 input --tcfile-in timecodes ...
x264 supports timecode input, which you can use to load MKV-style timecodes to turn any CFR input (e.g. Avisynth) into a proper-timestamped VFR one.

2. x264 input.mkv ...
x264, when using FFMS or LAVF input, will read the correct timestamps from input VFR MKV files (and MP4, FLV, and other formats that support variable framerate).

Now you can encode variable framerate files, even ones that are totally dedup'd to hell, without having to worry about getting the right bitrate.

[salty]

nice that you mentioned this. id probably not notice this in current commit. ill try them out when ill encode vfr this week.

[seven|x_x]

would it be wrong to assume that this works with both v1 and v2 timecodes?

[JEEB]

Originally Posted by seven|x_x

would it be wrong to assume that this works with both v1 and v2 timecodes?

Input should work with both, timecodes output (yes, x264 has it too) only does v2 (because of some obvious reasoning).

[Quarkboy]

Does this also work with mp4 output?

Clearly it wouldn't work with raw .264...

[Dark Shikari]

Originally Posted by Quarkboy

Does this also work with mp4 output?

Yes, all output container formats (including FLV) support VFR.

[Quarkboy]

Originally Posted by Dark Shikari

Yes, all output container formats (including FLV) support VFR.

Now if only youtube would handle vfr mp4's (or mkv for that matter, but I might have trouble convincing clients that mkv's are actually video files) correctly, that would make a heck of a lot of things I'm doing better quality.

But alas I just tried a test and youtube's transcoding fails miserably on anything vfr. I wonder if youtube would handle fake 120 fps avi's with no-ops?

[JEEB]

Originally Posted by Quarkboy

But alas I just tried a test and youtube's transcoding fails miserably on anything vfr. I wonder if youtube would handle fake 120 fps avi's with no-ops?

Yeah, the last I heard Youtube was using something mencoder-based, which would kill any VFR that'd be there (this can well be different now, though -- although the result seems to be the same as it used to be). On the 120fps stuff: As I know that 60fps stuff at least is just converted to 30fps, I'd think 120fps content would just get the same treatment... But you can always try how well it treats the victim in the case of a "pseudo-CFR" source.