[PD] gem codec basic review

Andrew Brouse brouse at music.mcgill.ca
Sun Dec 2 16:35:47 CET 2007

Hi Patrick,

As Marius noted, the best CODEC depends on what you are going to do with 
the video. The MPEG gang of CODECs (from MPEG-2 on through H-264) are very 
good for standard playback and have a good quality/file-size ratio. All 
visual CODECs use spatial coding - reduction of perceptual redundancies in 
the 2D plane of a given frame; but another way these CODECs achieve such 
good ratios is by using temporal coding to reduce frame to frame 
redundancies. They take a GOP (Group of Pictures, not an antediluvian 
near-extinct political party) and make decisions about what information is 
important. Some frames are fully represented and other frames are coded 
with reference to the ones around them. This saves a lot of space, but you 
do not have a full representation of each frame. During normal playback 
this is not a problem, but if you want to mess with the playback rate it 

If you want to do any scrubbing, varispeed or playing backwards of the 
video, you need a CODEC which does not use temporal compression. 
Photo-JPEG is in fact a very good choice in this case and if compressed at 
320 X 240 you get a good balance of file-size, picture quality and 
processor load. JPEG 2000 should also be a good choice (supported by 
QuickTime and there are libraries which support it on Linux but not sure 
if it will play in GEM). I have used DV video with good results and this 
may be a good option if you need high quality playback.

However, if you have unlimited bandwidth and storage, why not just go for 
uncompressed D-1 video? (~30M/s) ;)


On Fri, 30 Nov 2007, pd-list-request at iem.at wrote:

> hi,
> i am on linux running the very last version of gem from cvs. i am trying
> to find a good codec for gem. here's my basic research:
> ---------------------------------------
> the best codec for quicktime is jpeg:
> transcode -i yourvideo -y mov,null -F jpeg,,jpeg_quality=70 -o gem.mov
> gem cpu usage is 38%
> mplayer cpu usage is 27%
> ffplay cpu usage is 16%
> lqtplay cpu usage is 1% **
> ---------------------------------------
> for avi i tried ffmpeg / mjpeg:
> transcode -i yourvideo -y ffmpeg,null -F mjpeg -o gem.avi
> gem cpu usage is 33%
> mplayer cpu usage is 33%
> ffplay cpu usage is 22%
> ---------------------------------------
> the really best codec around is mpeg4:
> transcode -i yourvideo -y ffmpeg,null -F mpeg4 -o gem.avi
> gem cpu usage is: crashed**
> mplayer cpu usage is 16%
> ffplay cpu usage is 11%
> * lqtplay seems to make a excellent job for decoding is own codec. would
> it be possible to make a pix_qt based on the source of this player???
> ** anybody can test this codec? that would be my second choice... after
> lqtplay ported to gem...
> pat

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