ffmpeg中利用avcodec_encode_video2函数将YUV数据编码成.264数据:
/**
* Encode a frame of video.
*
* Takes input raw video data from frame and writes the next output packet, if
* available, to avpkt. The output packet does not necessarily contain data for
* the most recent frame, as encoders can delay and reorder input frames
* internally as needed.
*
* @param avctx codec context
* @param avpkt output AVPacket.
* The user can supply an output buffer by setting
* avpkt->data and avpkt->size prior to calling the
* function, but if the size of the user-provided data is not
* large enough, encoding will fail. All other AVPacket fields
* will be reset by the encoder using av_init_packet(). If
* avpkt->data is NULL, the encoder will allocate it.
* The encoder will set avpkt->size to the size of the
* output packet. The returned data (if any) belongs to the
* caller, he is responsible for freeing it.
*
* If this function fails or produces no output, avpkt will be
* freed using av_free_packet() (i.e. avpkt->destruct will be
* called to free the user supplied buffer).
* @param[in] frame AVFrame containing the raw video data to be encoded.
* May be NULL when flushing an encoder that has the
* CODEC_CAP_DELAY capability set.
* @param[out] got_packet_ptr This field is set to 1 by libavcodec if the
* output packet is non-empty, and to 0 if it is
* empty. If the function returns an error, the
* packet can be assumed to be invalid, and the
* value of got_packet_ptr is undefined and should
* not be used.
* @return 0 on success, negative error code on failure
*/
int avcodec_encode_video2(AVCodecContext *avctx,
AVPacket *avpkt,
const AVFrame *frame,
int *got_packet_ptr);
- *AVCodecContext avctx
用来保存编码参数等。
参数初始化举例:
pCodecCtx->bit_rate = 1024*1024;
pCodecCtx->width = m_nScreenWidth;
pCodecCtx->height = m_nScreenHeight;
pCodecCtx->time_base.num = 1;
pCodecCtx->time_base.den = 25;
pCodecCtx->gop_size = 25;
pCodecCtx->max_b_frames = 1;
pCodecCtx->pix_fmt = AV_PIX_FMT_YUV420P;
*AVPacket avpkt
输出的编码数据。*const AVFrame frame
该参数中包括输入的YUV数据等。*int got_packet_ptr
这个参数用于表明是否生成了编码数据。
需要说明的是: 不是输入一个YUV数据，就会输出一个编码数据。
编码器内部需要进行帧内预测、帧间预测等各种算法之后，才会输出一个编码数据。
调用实例:
AVCodec *pCodec = NULL;
AVCodecContext *pCodecCtx = NULL;
AVFrame *pFrame = NULL;
AVPacket pkt;
AVCodecID codec_id = AV_CODEC_ID_H264;
avcodec_register_all();
pCodec = avcodec_find_encoder(codec_id);
if (!pCodec)
{
printf("Codec not found\n");
return -1;
}
pCodecCtx = avcodec_alloc_context3(pCodec);
if (!pCodecCtx)
{
printf("Could not allocate video codec context\n");
return -1;
}
...
pFrame->data[0] = m_pYUVBuffer; // Y
pFrame->data[1] = m_pYUVBuffer + m_nUOffset; // U
pFrame->data[2] = m_pYUVBuffer + m_nVOffset; // V
av_init_packet(&pkt);
pkt.data = NULL; // packet data will be allocated by the encoder
pFrame->pts= ...;
/* encode the image */
nRet = avcodec_encode_video2(pCodecCtx, &pkt, pFrame, &got_packet);
if (nRet < 0)
{
printf("Error encoding frame\n");
return -1;
}
if (got_packet) // 获取到编码数据
{
{
printf("Succeed to encode frame: %5d\tsize:%5d\n", nVideoFrameCnt, pkt.size);
av_free_packet(&pkt);
}
}
Sleep(40);
}
调用avcodec_encode_video2输出的编码序列到底长啥样呢?
H.264编码序列 (ES码流)
(以上码流分析工具为:H264VideoESViewer)
可以看出序列的顺序:
SPS -> PPS -> SEI -> I帧 -> ...个P帧->SPS -> PPS -> SEI -> I帧 -> ...
另外需要注意的是:
SEI和I帧的start code是 0x00 0x00 0x01, 而其他的都是0x00 0x00 0x00 0x01。
