Strange issue with playback after converting 720p mkv to downscaled avi

[Phat J]

Hey,

I am encoding some videos from 720p x264 mkv format to xvid, and cutting the resolution down to 640x360.

I do this so I can play back these lesser quality versions on an older computer via my home network.

I'm using AVISynth to open the mkv files in VirtualDub, then I encode them as 2-pass XviD at 1600kbps, about half of the quality of the 720p videos.

The problem I have is playing some of the encodes on the other computer (winxp, 800mhz, 128mb ram) Most of them play completely fine.

On the slow computer, I open the problem files in media player classic, it just sits there with a black screen, 0:00 on the timer. With media player 9 and videolan, the playback stutters to the point it's unwatchable.

My question is, why would this happen to only a few videos? I am encoding the videos the same way (same codecs, bitrate, software) and most have no issues.
I have no issues playing back the original mkv files on my main PC, nor playing back any of the XviD versions on my main PC either.

I tried copying the problem files to the slow computer, then playing them back, instead of playing them over the network. Same issues, so it's not my network that's the problem.

Any ideas?

Thanks

[guns1inger]

Mediainfo the file and see if there is a difference. Perhaps run one of the AVI repair programs over it. It could be something as simple as glitch in the index.

[jagabo]

Also try using Bitrate Viewer to see bitrate spikes, GSpot to look for the number of consecutive b frames, GMC and QPel. Make sure the Xvid deblocking and deringing filters are disabled on the slow computer.

[Phat J]

I'm not sure what I'm looking for when I use MediaInfo, it shows the correct attributes that I encoded it at.
With Bitrate Viewer, the only odd thing I noticed is there's a huge spike of 24297 kbps 33 seconds into the video, not sure why it does that, the average bitrate is correct at 1595 kbps.
Rebuilding the index did not change the playback either.

Here are some other things I've tried, and nothing has helped:
-Encoding it as XviD again with a lower bitrate (1300kbps)
-Encoding it to WMV with the same settings
-Encoding the original MKV to huffy avi, then to XviD

Any other suggestions?

[jagabo]

Here are some other things I've tried, and nothing has helped:
-Encoding it as XviD again with a lower bitrate (1300kbps)
-Encoding it to WMV with the same settings
-Encoding the original MKV to huffy avi, then to XviD

Any other suggestions?

Replace the slow computer with a faster one?

Make sure there Xvid decoder is up to date. Make sure the graphics card is running optimally.

[yoda313]

Replace the slow computer?

Yes.

You could get a really cheap dvd player that is confirmed to play xvid files a the rates you are encoding to. Then simply burn them to dvdr and play them that way. Or by usb2 on a fat32 harddrive. There are a series of phillips dvd players that are highly recommended here from what I can tell. I'm sure they could be had for next to nothing.

[jagabo]

Another thing you might try is encoding with only I and P frames, no B frames. Be sure not to use QPel or GMC.

[Phat J]

Yeah I will replace the crappy laptop soon. All I use it for is watching videos, streaming audio, or reading pdf files in the bedroom.

Anyways, thanks for the other suggestions.

[jenera21]

Defragmenting may help. Although the in-built defragger may not be suitable. Try a good one like diskeeper. They've got a free trial on their website.

[jagabo]

Check the laptop's BIOS for a setting called Write Combining. Make sure it's enabled. Also check the graphics card's setup applet for that setting.