[FFmpeg-devel] [PATCH v4] H.264: reinitialize context on aspect ratio change as well

[Janusz Krzysztofik]

While using ffmpeg based vdr softdevice plugin for watching h.264 encoded live 
tv, I found that after correct picture aspect ratio setup on a new stream 
(channel) startup, any following picture aspect ratio changes were not 
processed. The same can be seen while playing vdr caputured samples of this 
transmission with ffplay.

This patch corrects the problem for me by reinitializing the decoder context 
on every valid aspect ratio change, not only size changes.

Created against ffmpeg svn revision 22565.
Tested with this revision ffplay.

Signed-off-by: Janusz Krzysztofik <jkrzyszt at tis.icnet.pl>
---
v4 changes:
- use av_cmp_q() instead of comparing numerators and denominators separately
  (thanks to Michael Niedermayer for advising this).

v3 changes:
- check for non-zero values of both new numerator and denominator to avoid 
  problems with some test samples (ie. cathedral-beta2-400extra-crop-avc.mp4).

v2 changes: none (refresh only)

--- trunk/libavcodec/h264.c.orig	2010-03-16 02:35:01.000000000 +0100
+++ trunk/libavcodec/h264.c	2010-03-16 02:39:04.000000000 +0100
@@ -1774,7 +1774,9 @@ static int decode_slice_header(H264Conte
         s->height= 16*s->mb_height - 4*FFMIN(h->sps.crop_bottom, 3);
 
     if (s->context_initialized
-        && (   s->width != s->avctx->width || s->height != s->avctx->height)) {
+        && (   s->width != s->avctx->width || s->height != s->avctx->height
+            || (h->sps.sar.num && h->sps.sar.den
+                && av_cmp_q(h->sps.sar, s->avctx->sample_aspect_ratio)))) {
         if(h != h0)
             return -1;   // width / height changed during parallelized decoding
         free_tables(h);