我正在尝试编码视频(目前使用h264编解码器,但如果更适合我的需要,其他编解码器也会很好),这样解码所需的数据可以在帧(包括第一帧)编码后直接使用(所以,我只想要I帧和P帧,没有B帧).
如何设置AVCodecContext以获取此类流?到目前为止,我的测试结果仍然总是导致avcodec_encode_video()在第一帧返回0.
//编辑:这是我目前AVCodecContext的设置代码:
static AVStream* add_video_stream(AVFormatContext *oc, enum CodecID codec_id, int w, int h, int fps)
{
AVCodecContext *c;
AVStream *st;
AVCodec *codec;
/* find the video encoder */
codec = avcodec_find_encoder(codec_id);
if (!codec) {
fprintf(stderr, "codec not found\n");
exit(1);
}
st = avformat_new_stream(oc, codec);
if (!st) {
fprintf(stderr, "Could not alloc stream\n");
exit(1);
}
c = st->codec;
/* Put sample parameters. */
c->bit_rate = 400000;
/* Resolution must be a multiple of two. */
c->width = w;
c->height = h;
/* 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. */
c->time_base.den = fps;
c->time_base.num = 1;
c->gop_size = 12; /* emit one intra frame every twelve frames at most */
c->codec = codec;
c->codec_type = AVMEDIA_TYPE_VIDEO;
c->coder_type = FF_CODER_TYPE_VLC;
c->me_method = 7; //motion estimation algorithm
c->me_subpel_quality = 4;
c->delay = 0;
c->max_b_frames = 0;
c->thread_count = 1; // more than one threads seem to increase delay
c->refs = 3;
c->pix_fmt = PIX_FMT_YUV420P;
/* Some formats want stream headers to be separate. */
if (oc->oformat->flags & AVFMT_GLOBALHEADER)
c->flags |= CODEC_FLAG_GLOBAL_HEADER;
return st;
}
但是使用这个avcodec_encode_video()将在返回任何字节之前缓冲13帧(之后,它将在每帧上返回字节).如果我将gop_size设置为0,那么avcodec_encode_video()将仅在第二帧传递给它后返回字节.我需要零延迟.
这个人显然是成功的(即使有更大的gop):http://mailman.videolan.org/pipermail/x264-devel/2009-May/005880.html,但我看不出他在做什么不同
最佳答案 对我来说,这段代码做了诀窍:
av_opt_set(context->priv_data, "tune", "zerolatency", 0);
(在打开上下文之前调用此函数.)