如何在C/C++中使用ffmpeg的黑框avfilter

Question

I want to capture the first-not-black frame for a video as its preview; I looked at sample which came with FFmpeg examples:

    /*
 * Copyright (c) 2010 Nicolas George
 * Copyright (c) 2011 Stefano Sabatini

/**
 * @file
 * API example for decoding and filtering
 * @example filtering_video.c
 */

But how can I use the "blackframe" filter in C/C++?

Answer 1

Recently, I am also solving the problem of how to detect black frames. Refer to vf_ blackframe.c, when the frame is judged as a black frame, frame->metadata will add a value "lavfi.blackframe.pblack"

set filter_describe as

const char *str_filter_describe = "[in]blackframe=95:30[out]";

whether it is black frame

if (av_buffersrc_add_frame(_buffersrc_ctx, frame)< 0)
{
    printf("error");
}
while (ture)
{
    int ret = av_buffersink_get_frame_flags(_buffersink_ctx, frame, 0);
    if (ret < 0)
    {
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
            ret = 0;
        break;
    }
};

if (auto e = av_dict_get(frame->metadata, "lavfi.blackframe.pblack", NULL,AV_DICT_MATCH_CASE){
    if (strcmp("0", e->value) != 0){
        printf("this is a black frame!!! amount:%s,pts:%ld", e->value, frame->pts);

        /*post a message or do something */
        
        //chage it value to 0
        av_dict_set(&frame->metadata, "lavfi.blackframe.pblack", temp, 0);
    }}

and make sure compile ffmpeg with --enable-filter=blackframe