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ffmpeg插入sei实践

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站长
· 阅读数 57

本文章主要讲述如何修改ffmpeg源码,实现在每个关键帧中插入sei。

原始Bsf

BitStream Filter(码流过滤)的缩写为bsf,它的作用是,在不做码流解码的前提下,对已经编码后的比特流做特定的修改、调整。

bsf h264_metadata的调用

使用ffmpeg工具时,可以使用比特流过滤器。基本的filter调用格式如下:

ffmpeg -i INPUT -c:v copy -bsf:v filter1[=opt1=str1:opt2=str2][,filter2] OUTPUT

可以使用 h264_metadata比特流过滤器添加SEI。下面示例命令添加了类型为未注册的用户数据的SEI,其中uuid为"086f3693-b7b3-4f2c-9653-21492feee5b8",payload内容为"hello":

./ffmpeg  -I oceans.h264 -c:v copy -bsf:v h264_metadata=sei_user_data='086f3693-b7b3-4f2c-9653-21492feee5b8+hello' oceans.sei.h264

Bsf修改

修改文件为h264_metadata_bsf.c

查找出关键帧

from

    has_sps = 0;
    for (i = 0; i < au->nb_units; i++) {
        if (au->units[i].type == H264_NAL_SPS) {
            err = h264_metadata_update_sps(bsf, au->units[i].content);
            if (err < 0)
                goto fail;
            has_sps = 1;
        }
    }

to

    int has_idr = 0;
    has_sps = 0;
    for (i = 0; i < au->nb_units; i++) {
        if (au->units[i].type == H264_NAL_SPS) {
            err = h264_metadata_update_sps(bsf, au->units[i].content);
            if (err < 0)
                goto fail;
            has_sps = 1;
        }
        if (au->units[i].type == H264_NAL_IDR_SLICE) {
            has_idr = 1;
        }
    }

判断是关键帧

from

    // Only insert the SEI in access units containing SPSs, and also
    // unconditionally in the first access unit we ever see.
    if (ctx->sei_user_data && (has_sps || !ctx->done_first_au)) {

to

    // Only insert the SEI in access units containing IDRs, and also
    // unconditionally in the first access unit we ever see.
    if (ctx->sei_user_data && (has_idr || !ctx->done_first_au)) {

在关键帧后插入一帧SEI

当参数为“-bsf:v h264_metadata=sei_user_data='086f3693-b7b3-4f2c-9653-21492feee5b8+{timestamp}'”时插入当前时间戳。

解析出的SEI信息为"ts:timestamp"精确到毫秒

from

    udu->data        = udu->data_ref->data;
    udu->data_length = len + 1;
    memcpy(udu->data, ctx->sei_user_data + i + 1, len + 1);

to

    udu->data        = udu->data_ref->data;
    udu->data_length = len + 1;
    memcpy(udu->data, ctx->sei_user_data + i + 1, len + 1);
            
    //convert to Timestamp
    if(strcmp(udu->data, "{timestamp}") == 0){
        char mark[] = "ts:";
        long timestamp = av_gettime() / 1000;
        char result[20];
        sprintf(result, "%s%ld", mark, timestamp);
                
        udu->data        = result;
        udu->data_length = strlen(result) + 1;
    }

调试方法

使用xcode

使用方法

-bsf:v h264_metadata=sei_user_data='086f3693-b7b3-4f2c-9653-21492feee5b8+{timestamp}'

栗子:

-stream_loop -1 -i video.mp4  -c:a aac -c:v libx264 -bsf:v h264_metadata=sei_user_data='086f3693-b7b3-4f2c-9653-21492feee5b8+{timestamp}' -f flv rtmp://demo-push.cn/live/11

参考资料

转载自:https://juejin.cn/post/7216153056282607653
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