The VideoLAN Forums

so, playback of h264 files on my 1.5ghz mac mini is really cpu intensive. Playing back a dvd resolution file (720x400) takes about 95% of the cpu. The same file in vlc on windows (pentium m 1.4 ghz) takes about 20% of the cpu. What gives? both machines are equipped with radeon video cards with 32mb ram (laptop a radeon 9000, mini 9200). Everything is up to date on both systems. Doesn't matter if the files were encoded with x264 or recode. I just can't figure out why the cpu use is so high under osx. Do these numbers jive with everyone else's experiences?

ive already asked the same question and the answer is simple. for h264 vlc relies on ffmpeg for replay and ffmpeg is highly optimized for x86, sse, sse2.

the ffmpeg altivec parts are getting better day by day, however on my powerbook videos encoded with recode are nearly unplayable, however a memory leak that caused vlc to crash with h264 videos was fixed in the last nightlies.

but... ive found a way for playing back without hassle. in the preference you could set "skip the loop filter for h.264 decoding" to - skip all. this lowers the quality however its full playable. ive played with this setting to find a good compromise between cpu needs and quality.

I found that lowering the "framerate" (in Preferences>Input/Codecs>Demuxers>H264) to about 16 helps a lot too. It doesn't actually lower the framerate -- the video is smooth and syncs up with the audio just fine.

haifischjunge -- where is that preference?

it's really amazing that the performance is that poor. seems like that much of a difference between the two machines can't simply be a compiler optimization or something, but I guess that's it. Will the switch to osx86 help?

@ Guest: Yes, this will probably help. It's not about compiler optimisations btw.: ffmpeg uses certain velocity extensions (as mentioned: AltiVec, SSE, etc.). The SSE-units are x86 only and very well supported, while AltiVec is ppc-only and only little optimised, since most of the ffmpeg-devs are using x86-PCs.

It's really seems like h264 tend to crash VLC under OS X :

I've got some MKV with h264/AAC/ASS and I use the latest VLC-Trunk (18/01/06)

Each time I try to read them I got some crashing like :

[00000291] ffmpeg decoder error: more than 5 seconds of late video -> dropping frame (computer too slow ?)
h264.c:2610: failed assertion `pic->data[0]'

I don't have actually better crash log.. It's taken from the console, vlc seems to not writing a crashlog :/

That's a typical error in case that your computer is too slow. ffmpeg's h264 decoder isn't finished. That's it does just crash then.
You might want to try out a nightly build, which could handle this a bit better, but is 10.4 only at the moment.