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avformat/matroskaenc: only write AlphaMode for VP8 and VP9

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AlphaMode should indicate whether the BlockAdditional Element with BlockAddID
of "1" contains Alpha data, as defined by to the Codec Mapping for the `CodecID`.

Only VP8 and VP9 Codec Mappings define this, so writing it for all codecs with
a pixel format of YUVA420P, or for codecs other than VP8/VP9 (if the alpha_mode
metadata entry was set) was wrong.

Signed-off-by: Marton Balint <cus@passwd.hu>
This commit is contained in:
Marton Balint
2026-02-07 00:19:47 +01:00
parent 3ec03b847b
commit 9515cb236b
1 changed files with 15 additions and 4 deletions
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19
libavformat/matroskaenc.c
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@@ -19,6 +19,7 @@
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <stdbool.h>
#include <stdint.h>
#include "config_components.h"
@@ -1787,11 +1788,23 @@ static void mkv_write_blockadditionmapping(AVFormatContext *s, const MatroskaMux
#endif
}
static bool codec_has_blockadditional_alpha(AVFormatContext *s, const AVStream *st,
const AVCodecParameters *par)
{
const AVDictionaryEntry *tag;
if (par->codec_id != AV_CODEC_ID_VP8 &&
par->codec_id != AV_CODEC_ID_VP9)
return false;
if (par->format == AV_PIX_FMT_YUVA420P)
return true;
return ((tag = av_dict_get(st->metadata, "alpha_mode", NULL, 0)) ||
(tag = av_dict_get( s->metadata, "alpha_mode", NULL, 0))) && strtol(tag->value, NULL, 0);
}
static int mkv_write_track_video(AVFormatContext *s, MatroskaMuxContext *mkv,
const AVStream *st, const AVCodecParameters *par,
AVIOContext *pb)
{
const AVDictionaryEntry *tag;
int display_width_div = 1, display_height_div = 1;
uint8_t color_space[4], projection_private[20];
const AVPacketSideData *sd;
@@ -1815,9 +1828,7 @@ static int mkv_write_track_video(AVFormatContext *s, MatroskaMuxContext *mkv,
if (ret < 0)
return ret;
if (par->format == AV_PIX_FMT_YUVA420P ||
((tag = av_dict_get(st->metadata, "alpha_mode", NULL, 0)) ||
(tag = av_dict_get( s->metadata, "alpha_mode", NULL, 0))) && strtol(tag->value, NULL, 0))
if (codec_has_blockadditional_alpha(s, st, par))
ebml_writer_add_uint(&writer, MATROSKA_ID_VIDEOALPHAMODE, 1);
sd = av_packet_side_data_get(par->coded_side_data,