我正在逐帧转码视频并使用 x264+ffmpeg 进行编码。原始视频播放良好，但我转码视频的前几帧显示灰色伪影。我知道这是因为时间压缩，这些伪影在几帧后消失了。
请看这两张图片，它们是第一帧和第二帧。第三帧正常（即没有灰色伪影，也没有像第二帧那样模糊）
如何强制第一帧成为关键帧（即在我的输出视频中完全编码），以使这些伪影不显示？
编辑 - 更多细节
这是我正在做的更多细节。我使用 bit form differents 教程逐帧读取视频并将每一帧重新编码为新视频。我的编码参数如下：
avcodec_get_context_defaults3(c, *codec);
c->codec_id = codec_id;
c->bit_rate = output_bitrate;
/* Resolution must be a multiple of two. */
c->width = output_width;
c->height = output_height;
/* timebase: This is the fundamental unit of time (in seconds) in terms
* of which frame timestamps are represented. For fixed-fps content,
* timebase should be 1/framerate and timestamp increments should be
* identical to 1. */
st->r_frame_rate.num = output_framerate_num;
st->r_frame_rate.den = output_framerate_den;
c->time_base.den = output_timebase_den;
c->time_base.num = output_timebase_num;
c->gop_size = 3; /* emit one intra frame every twelve frames at most */
c->pix_fmt = STREAM_PIX_FMT;
if (c->codec_id == AV_CODEC_ID_MPEG2VIDEO) {
/* just for testing, we also add B frames */
c->max_b_frames = 2;
}
if (c->codec_id == AV_CODEC_ID_MPEG1VIDEO) {
/* Needed to avoid using macroblocks in which some coeffs overflow.
* This does not happen with normal video, it just happens here as
* the motion of the chroma plane does not match the luma plane. */
c->mb_decision = 2;
}
c->max_b_frames = 2;
c->scenechange_threshold = 0;
c->rc_buffer_size = 0;
c->me_method = ME_ZERO;
然后我处理每一帧，可能在那里做错了什么。解码位：
while(av_read_frame(gFormatCtx, &packet)>=0) {
// Is this a packet from the video stream?
if(packet.stream_index==gVideoStreamIndex) {
// Decode video frame
avcodec_decode_video2(gVideoCodecCtx, pCurrentFrame, &frameFinished, &packet);
// Did we get a video frame?
if(frameFinished) {
[...]
if(firstPts == -999) /*Initial value*/
firstPts = packet.pts;
deltaPts = packet.pts - firstPts;
double seconds = deltaPts*av_q2d(gFormatCtx->streams[gVideoStreamIndex]->time_base);
[...]
muxing_writeVideoFrame(pCurrentFrame, packet.pts);
}
}
}
实际写法：
int muxing_writeVideoFrame(AVFrame *frame, int64_t pts)
{
frameCount = frameCount +1;
if(frameCount > 0)
{
if (video_st)
video_pts = (double)video_st->pts.val * video_st->time_base.num /
video_st->time_base.den;
else
video_pts = 0.0;
if (video_st && !(video_st && audio_st && audio_pts < video_pts))
{
frame->pts = pts;//av_rescale_q(frame_count, video_st->codec->time_base, video_st->time_base);
write_video_frame(oc, video_st, frame);
}
}
return 0;
}
static int write_video_frame(AVFormatContext *oc, AVStream *st, AVFrame *frame)
{
int ret;
static struct SwsContext *sws_ctx;
//LOGI(10, frame_count);
AVCodecContext *c = st->codec;
/* encode the image */
AVPacket pkt;
int got_output;
av_init_packet(&pkt);
pkt.data = NULL; // packet data will be allocated by the encoder
pkt.size = 0;
ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding video frame: %s\n", av_err2str(ret));
exit(1);
}
/* If size is zero, it means the image was buffered. */
if (got_output) {
if (c->coded_frame->key_frame)
pkt.flags |= AV_PKT_FLAG_KEY;
pkt.stream_index = st->index;
/* Write the compressed frame to the media file. */
ret = av_interleaved_write_frame(oc, &pkt);
} else {
ret = 0;
}
if (ret != 0) {
LOGI(10, av_err2str(ret));
exit(1);
}
frame_count++;
return got_output;
}