Add slice-based parallel H.264 decoding

Patch by Andreas Öman % andreas A olebyn P nu %
NB: depends on having a thread library activated at config time, and on
having a source encoded with multiple slices
Original threads:
date: May 18, 2007 11:00 PM
subject: [FFmpeg-devel] Parallelized h264 proof-of-concept
date: Jun 15, 2007 10:10 PM
subject: [FFmpeg-devel] [PATCH] h264 parallelized, (was: Parallelized h264 proof-of-concept)
date: Jun 25, 2007 7:02 PM
subject: Re: [FFmpeg-devel] [PATCH] h264 parallelized

Originally committed as revision 10407 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264.h

@@ -380,6 +380,35 @@ typedef struct H264Context{
     const uint8_t *field_scan8x8_cavlc_q0;
 
     int x264_build;
+
+    /**
+     * @defgroup multithreading Members for slice based multithreading
+     * @{
+     */
+    struct H264Context *thread_context[MAX_THREADS];
+
+    /**
+     * current slice number, used to initalize slice_num of each thread/context
+     */
+    int current_slice;
+
+    /**
+     * Max number of threads / contexts.
+     * This is equal to AVCodecContext.thread_count unless
+     * multithreaded decoding is impossible, in which case it is
+     * reduced to 1.
+     */
+    int max_contexts;
+
+    /**
+     *  1 if the single thread fallback warning has already been
+     *  displayed, 0 otherwise.
+     */
+    int single_decode_warning;
+
+    int last_slice_type;
+    /** @} */
+
 }H264Context;
 
 #endif /* H264_H */

libavcodec/mpegvideo.c

@@ -418,7 +418,7 @@ void MPV_decode_defaults(MpegEncContext *s){
  */
 int MPV_common_init(MpegEncContext *s)
 {
-    int y_size, c_size, yc_size, i, mb_array_size, mv_table_size, x, y;
+    int y_size, c_size, yc_size, i, mb_array_size, mv_table_size, x, y, threads;
 
     s->mb_height = (s->height + 15) / 16;
 
@@ -587,12 +587,16 @@ int MPV_common_init(MpegEncContext *s)
     s->context_initialized = 1;
 
     s->thread_context[0]= s;
-    for(i=1; i<s->avctx->thread_count; i++){
+    /* h264 does thread context setup itself, but it needs context[0]
+     * to be fully initialized for the error resilience code */
+    threads = s->codec_id == CODEC_ID_H264 ? 1 : s->avctx->thread_count;
+
+    for(i=1; i<threads; i++){
         s->thread_context[i]= av_malloc(sizeof(MpegEncContext));
         memcpy(s->thread_context[i], s, sizeof(MpegEncContext));
     }
 
-    for(i=0; i<s->avctx->thread_count; i++){
+    for(i=0; i<threads; i++){
         if(init_duplicate_context(s->thread_context[i], s) < 0)
            goto fail;
         s->thread_context[i]->start_mb_y= (s->mb_height*(i  ) + s->avctx->thread_count/2) / s->avctx->thread_count;