static int mov_write_mvhd_tag(AVIOContext *pb, MOVMuxContext *mov)
{
int max_track_id = 1, i;
int64_t max_track_len = 0;
int version;
for (i = 0; i < mov->nb_streams; i++) {
if (mov->tracks[i].entry > 0 && mov->tracks[i].timescale) {
int64_t max_track_len_temp = av_rescale_rnd(
calc_pts_duration(mov, &mov->tracks[i]),
MOV_TIMESCALE,
mov->tracks[i].timescale,
AV_ROUND_UP);
if (max_track_len < max_track_len_temp)
max_track_len = max_track_len_temp;
if (max_track_id < mov->tracks[i].track_id)
max_track_id = mov->tracks[i].track_id;
}
}
/* If using delay_moov, make sure the output is the same as if no
* samples had been written yet. */
if (mov->flags & FF_MOV_FLAG_EMPTY_MOOV) {
max_track_len = 0;
max_track_id = 1;
}
version = max_track_len < UINT32_MAX ? 0 : 1; //version 0 最大支持UINT32_MAX的视频长度，若是时长更长需要用64bit表示，设置为version 1
avio_wb32(pb, version == 1 ? 120 : 108); /* size */
ffio_wfourcc(pb, "mvhd");
avio_w8(pb, version);
avio_wb24(pb, 0); /* flags */
if (version == 1) {
avio_wb64(pb, mov->time);
avio_wb64(pb, mov->time);
} else {
avio_wb32(pb, mov->time); /* creation time */
avio_wb32(pb, mov->time); /* modification time */
}
avio_wb32(pb, MOV_TIMESCALE);
(version == 1) ? avio_wb64(pb, max_track_len) : avio_wb32(pb, max_track_len); /* duration of longest track */
avio_wb32(pb, 0x00010000); /* reserved (preferred rate) 1.0 = normal */
avio_wb16(pb, 0x0100); /* reserved (preferred volume) 1.0 = normal */
avio_wb16(pb, 0); /* reserved */
avio_wb32(pb, 0); /* reserved */
avio_wb32(pb, 0); /* reserved */
/* Matrix structure */
write_matrix(pb, 1, 0, 0, 1, 0, 0); //
avio_wb32(pb, 0); /* reserved (preview time) */
avio_wb32(pb, 0); /* reserved (preview duration) */
avio_wb32(pb, 0); /* reserved (poster time) */
avio_wb32(pb, 0); /* reserved (selection time) */
avio_wb32(pb, 0); /* reserved (selection duration) */
avio_wb32(pb, 0); /* reserved (current time) */
avio_wb32(pb, max_track_id + 1); /* Next track id */
return 0x6c;
}
主要写入如下值
-
- 版本
- 创建时间
- 播放速度
- 默认音量
- write_matrix 写入视频变换矩阵，具体作用待分析。