[Ffmpeg-devel] Comparison of gray codecs

[Kostya]

On Tue, Sep 19, 2006 at 07:01:35PM +0200, Philippe De Muyter wrote:
> Hi all,
> 
> I have tried to compress a 2.1G grayscale (y8) rawvideo 640x480 30fps video
> (about 4 minutes) with all codecs found in the ffmpeg distro (SVN-r6290),
> with the following command line :
> 
> 	./ffmpeg -y -i /tmp/rawvideo.avi -vcodec $codec /tmp/gray-$codec.avi
> 
> Below are the results.
> 
> All comparisons are made using an avi format output file :
> 
> 		Announced		Replay
> 		Output			Quality
[... skipped most of results ...]
> huffyuv		yuv422p		2.0G	Good	0m46.260s
> jpegls		gray		-	-	decode crash
> ljpeg		gray		-	-	colorspace not supported
> mjpeg		yuvj420p	63M	Bad	0m33.014s
> 
> Summary :
> 
> None of the tested codec succeeds in compressing gray video preserving
> gray pixels.
> 
[summary skipped]

Here is a small patch which fixes grayscale JPEG-LS decoding so now you have the
codec which supports grayscale encoding and is lossless or near-lossless.
For lossy compression try passing '-pred x' option where 1 <= x <= 3. It won't
result in blockiness too.

I hope Michael will approve this patch and it will be applied.
-------------- next part --------------
Index: mjpeg.c
===================================================================
--- mjpeg.c	(revision 6151)
+++ mjpeg.c	(working copy)
@@ -2039,6 +2039,7 @@
                         return -1;
                     break;
                 case EOI:
+                    s->cur_scan = 0;
                     if ((s->buggy_avid && !s->interlaced) || s->restart_interval)
                         break;
 eoi_parser: