the top_field_first bit is only used to indicate the field order
when the picture is a frame picture (which consists of two fields)
but not when it is a field picture (which consists of one single
top or bottom field).
Signed-off-by: Tom Yan <tom.t...@gmail.com>
---
libavcodec/mpegvideo_parser.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/libavcodec/mpegvideo_parser.c b/libavcodec/mpegvideo_parser.c
index c5dc867d24..2ddcdb0f37 100644
--- a/libavcodec/mpegvideo_parser.c
+++ b/libavcodec/mpegvideo_parser.c
@@ -108,7 +108,7 @@ static void mpegvideo_extract_headers(AVCodecParserContext
*s,
uint32_t start_code;
int frame_rate_index, ext_type, bytes_left;
int frame_rate_ext_n, frame_rate_ext_d;
- int top_field_first, repeat_first_field, progressive_frame;
+ int picture_structure, top_field_first, repeat_first_field,
progressive_frame;
int horiz_size_ext, vert_size_ext, bit_rate_ext;
int did_set_size=0;
int set_dim_ret = 0;
@@ -181,6 +181,7 @@ static void mpegvideo_extract_headers(AVCodecParserContext
*s,
break;
case 0x8: /* picture coding extension */
if (bytes_left >= 5) {
+ picture_structure = buf[2] & 0x3;
top_field_first = buf[3] & (1 << 7);
repeat_first_field = buf[3] & (1 << 1);
progressive_frame = buf[4] & (1 << 7);
@@ -199,7 +200,9 @@ static void mpegvideo_extract_headers(AVCodecParserContext
*s,
}
if (!pc->progressive_sequence && !progressive_frame) {
- if (top_field_first)
+ /* top_field_first is mandated to be 0 when
+ picture_structure is not 3 (i.e. not a frame
picture) */
+ if (top_field_first || picture_structure == 1)
s->field_order = AV_FIELD_TT;
else
s->field_order = AV_FIELD_BB;
--
2.35.1
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