How can I optimize playback smoothness with XviD?

[diamondsw]

I have been having problems with XviD movies I create having significant playback problems - frames get dropped, they play particularly slowly, stuttering audio, etc. Are there any settings I should be focusing on to make it "easier" for my various players to decode, or is this simply a case of not having enough horsepower, period? I'd like to maintain video quality, but I can certainly accept a larger file as a trade-off.

I know that all of the frames and audio data is there by playing it in slow motion, but something about my settings seems to be overpowering my computer. Now, said computer is rather slow - an iBook G3/800Mhz, so some of this is to be expected. However, I have several XviD files I've downloaded that playback fine at similar resolutions, so I think I've set something improperly that's causing XviD to do a lot more work than it should be.

Here's some background on what I'm trying to accomplish:

• I have several anime fansubs where the author decided to use WMV9 video in an AVI container, which is unplayable on Mac OS X or any non-x86 Linux platform (even playing it on Linux-x86 is difficult). The original resolution is a decent 704 x 396, and they are on average about 25 minutes long.
• I am using VirtualDub 1.6.10 and XviD 1.0.3 on Windows XP to perform my transcoding. For my initial tests, I performed a full-processing video encode with default XviD settings for a single pass, and set the bitrate to 1024, and quantatizer to 4.00 (I really wish I knew what that setting meant!). Audio was set to direct copy (already in MP3 format).
• This took a long time, but the resulting movie looked very similar to the original when performing some spot checks, and at a greatly reduced file size - 133MB instead of the original 250MB (which makes me a bit suspicious). [I did try a two-pass encode, but I could not see much of a visual difference, and I deleted it. I also tried a single pass encode with a bitrate of 2048, and this resulted in a 488MB file that also did not look significantly different - I deleted it as well.]
• The resulting file technically plays in Windows, and on Mac OS X in Quicktime, VLC, and MPlayer, but with varying degress of success. In Windows the video stops playing for a couple seconds every so often as my computer presumably falls behind. In Quicktime, it drops frames like crazy (much worse than on Windows). MPlayer plays everything, but slows down to about 1/2 speed and loses audio-video sync. VLC comes close to playing it, but is still dropping frames, although less severely.

[celtic_druid]

VLC should be able to handle WMV9 (VC-1) under OSX.
Default settings have bframes enabled from recollection. You could try disabling them however with your specs I would have thought it would playback fine with mplayer at least.

[diamondsw]

I'll try disabling b-frames - what impact will that have on the final movie? I'm very new at the codec terminology.

Sadly, VLC does not support WMV9 video - it's a fairly well-known (and sad) state of affairs that nothing on Mac OS X can play WMV9 in an AVI container. Windows Media Player won't touch it based on the AVI container; nothing else on the system can read the video track. here's VLC's response (latest version - 0.8.2):

main: no suitable decoder module for fourcc `WMV3'.
VLC probably does not support this sound or video format.

[celtic_druid]

Well disabling bframes will reduce the amount of power required to decode. Also if something is dropping frames, then they would generally be bframes. For a given size it should also result in lower quality.

About VLC, try a newer build maybe as I am pretty sure that VLC has a working VC-1 decoder which should work fine for WMV9.

If you compile it yourself then you can make sure that VC-1 support is enabled.