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h264: skip start code search if the size of the nal unit is known

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Start code emulation prevention is only required in Annex B bytestream
packed NAL units. For other coding formats the size is already known.
Looking for a start code prefix can result in false positives like in
http://streams.videolan.org/streams/mp4/Mr_MrsSmith-h264_aac.mp4
which has a false positive in the SPS.
This commit is contained in:
Janne Grunau 2011-12-18 22:42:36 +01:00
parent 2e7905eee8
commit 87eebb3454
3 changed files with 14 additions and 4 deletions
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11
libavcodec/h264.c
View File

@ -137,7 +137,10 @@ int ff_h264_check_intra_pred_mode(H264Context *h, int mode){
return mode; return mode;
} }
const uint8_t *ff_h264_decode_nal(H264Context *h, const uint8_t *src, int *dst_length, int *consumed, int length){ const uint8_t *ff_h264_decode_nal(H264Context *h, const uint8_t *src,
int *dst_length, int *consumed, int length,
int nalsize_known)
{
int i, si, di; int i, si, di;
uint8_t *dst; uint8_t *dst;
int bufidx; int bufidx;
@ -148,6 +151,9 @@ const uint8_t *ff_h264_decode_nal(H264Context *h, const uint8_t *src, int *dst_l
src++; length--; src++; length--;
if (nalsize_known) {
i = length;
} else
#if HAVE_FAST_UNALIGNED #if HAVE_FAST_UNALIGNED
# if HAVE_FAST_64BIT # if HAVE_FAST_64BIT
# define RS 7 # define RS 7
@ -3789,7 +3795,8 @@ static int decode_nal_units(H264Context *h, const uint8_t *buf, int buf_size){
hx = h->thread_context[context_count]; hx = h->thread_context[context_count];
ptr= ff_h264_decode_nal(hx, buf + buf_index, &dst_length, &consumed, next_avc - buf_index); ptr= ff_h264_decode_nal(hx, buf + buf_index, &dst_length, &consumed,
next_avc - buf_index, !!nalsize);
if (ptr==NULL || dst_length < 0){ if (ptr==NULL || dst_length < 0){
return -1; return -1;
} }

5
libavcodec/h264.h
View File

@ -610,9 +610,12 @@ int ff_h264_decode_picture_parameter_set(H264Context *h, int bit_length);
* @param consumed is the number of bytes used as input * @param consumed is the number of bytes used as input
* @param length is the length of the array * @param length is the length of the array
* @param dst_length is the number of decoded bytes FIXME here or a decode rbsp tailing? * @param dst_length is the number of decoded bytes FIXME here or a decode rbsp tailing?
* @param nalsize_known skip start code search if the size of the nalu is known
* @return decoded bytes, might be src+1 if no escapes * @return decoded bytes, might be src+1 if no escapes
*/ */
const uint8_t *ff_h264_decode_nal(H264Context *h, const uint8_t *src, int *dst_length, int *consumed, int length); const uint8_t *ff_h264_decode_nal(H264Context *h, const uint8_t *src,
int *dst_length, int *consumed, int length,
int nalsize_known);
/** /**
* Free any data that may have been allocated in the H264 context like SPS, PPS etc. * Free any data that may have been allocated in the H264 context like SPS, PPS etc.

2
libavcodec/h264_parser.c
View File

@ -144,7 +144,7 @@ static inline int parse_nal_units(AVCodecParserContext *s,
src_length = 20; src_length = 20;
break; break;
} }
ptr= ff_h264_decode_nal(h, buf, &dst_length, &consumed, src_length); ptr= ff_h264_decode_nal(h, buf, &dst_length, &consumed, src_length, 0);
if (ptr==NULL || dst_length < 0) if (ptr==NULL || dst_length < 0)
break; break;