ffmpeg # 判断AVPacket是否为关键帧

如何判断当前AVPacket是否为关键帧呢?
答案是: 通过AVPacket中的flags来判断。

typedef struct AVPacket {
...
    /**
     * A combination of AV_PKT_FLAG values
     */
    int   flags;
...
}

AV_PKT_FLAG values定义如下：

#define AV_PKT_FLAG_KEY     0x0001 ///< The packet contains a keyframe
#define AV_PKT_FLAG_CORRUPT 0x0002 ///< The packet content is corrupted
/**
 * Flag is used to discard packets which are required to maintain valid
 * decoder state but are not required for output and should be dropped
 * after decoding.
 **/
#define AV_PKT_FLAG_DISCARD   0x0004

其中AV_PKT_FLAG_KEY用来表示是否为关键帧。

• 赋值

AVPacket *pkt;

...
pkt.flags |= AV_PKT_FLAG_KEY;

• 判断是否为关键帧

AVPacket *pkt;

...

if (pkt->flags & AV_PKT_FLAG_KEY) // is keyframe
{
...
}
...

另一个例子:

AVPacket pkt;
...
for (;;) {
            int read_status;
            do {
                read_status = av_read_frame(s, &pkt);
            } while (read_status == AVERROR(EAGAIN));
            if (read_status < 0)
                break;
            if (stream_index == pkt.stream_index && pkt.dts > timestamp) {
                if (pkt.flags & AV_PKT_FLAG_KEY) {
                    av_packet_unref(&pkt);
                    break;
                }
              ...
            }
            av_packet_unref(&pkt);
        }