参考链接
- FFmpeg源代码简单分析：avcodec_encode_video()_雷霄骅的博客-CSDN博客_avcodec_encode_video2
avcodec_encode_video()
- 该函数用于编码一帧视频数据。
- 函数已被弃用
- 参考链接：FFmpeg 新旧版本编码 API 的区别_zouzhiheng的博客-CSDN博客
send_frame 和 receive_packet 例子
static void encode(AVCodecContext *enc_ctx, AVFrame *frame, AVPacket *pkt,FILE *outfile)
{int ret;/* send the frame to the encoder */if (frame)printf("Send frame %3"PRId64"\n", frame->pts);ret = avcodec_send_frame(enc_ctx, frame);if (ret < 0) {fprintf(stderr, "Error sending a frame for encoding\n");exit(1);}while (ret >= 0) {ret = avcodec_receive_packet(enc_ctx, pkt);if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)return;else if (ret < 0) {fprintf(stderr, "Error during encoding\n");exit(1);}printf("Write packet %3"PRId64" (size=%5d)\n", pkt->pts, pkt->size);fwrite(pkt->data, 1, pkt->size, outfile);av_packet_unref(pkt);}
}
- avcodec_encode_video一个函数即可完成编码操作，编码成功后可直接使用压缩后的数据。新版 API 需要两个函数一起使用，一个 send，一个 receive，分别用于发送原始视频数据、获取编码后的数据；具体在哪里完成了编码动作，暂时未知。
- avcodec_encode_video 一次编码动作对应 0 个或 1 个 AVFrame 和 0 个或 1 个 AVPacket。新本 API 一次编码动作对应 0 个或 1 个 AVFrame 和 0 个或多个 AVPacket。
avcodec_send_frame
- avcodec_send_frame 的声明如下：
/*** Supply a raw video or audio frame to the encoder. Use avcodec_receive_packet()* to retrieve buffered output packets.** @param avctx codec context* @param[in] frame AVFrame containing the raw audio or video frame to be encoded.* Ownership of the frame remains with the caller, and the* encoder will not write to the frame. The encoder may create* a reference to the frame data (or copy it if the frame is* not reference-counted).* It can be NULL, in which case it is considered a flush* packet. This signals the end of the stream. If the encoder* still has packets buffered, it will return them after this* call. Once flushing mode has been entered, additional flush* packets are ignored, and sending frames will return* AVERROR_EOF.** For audio:* If AV_CODEC_CAP_VARIABLE_FRAME_SIZE is set, then each frame* can have any number of samples.* If it is not set, frame->nb_samples must be equal to* avctx->frame_size for all frames except the last.* The final frame may be smaller than avctx->frame_size.* @return 0 on success, otherwise negative error code:* AVERROR(EAGAIN): input is not accepted in the current state - user* must read output with avcodec_receive_packet() (once* all output is read, the packet should be resent, and* the call will not fail with EAGAIN).* AVERROR_EOF: the encoder has been flushed, and no new frames can* be sent to it* AVERROR(EINVAL): codec not opened, it is a decoder, or requires flush* AVERROR(ENOMEM): failed to add packet to internal queue, or similar* other errors: legitimate encoding errors*/
int avcodec_send_frame(AVCodecContext *avctx, const AVFrame *frame);-
从注释中可以看出，这个函数用于发送原始的视频/音频数据给编码器编码，参数 AVFrame 同样可以为 NULL 以刷新编码器。
int attribute_align_arg avcodec_send_frame(AVCodecContext *avctx, const AVFrame *frame)
{AVCodecInternal *avci = avctx->internal;int ret;if (!avcodec_is_open(avctx) || !av_codec_is_encoder(avctx->codec))return AVERROR(EINVAL);if (avci->draining)return AVERROR_EOF;if (avci->buffer_frame->buf[0])return AVERROR(EAGAIN);if (!frame) {avci->draining = 1;} else {ret = encode_send_frame_internal(avctx, frame);if (ret < 0)return ret;}if (!avci->buffer_pkt->data && !avci->buffer_pkt->side_data) {ret = encode_receive_packet_internal(avctx, avci->buffer_pkt);if (ret < 0 && ret != AVERROR(EAGAIN) && ret != AVERROR_EOF)return ret;}avctx->frame_number++;return 0;
}
avcodec_receive_packet
- avcodec_receive_packet 则用于获取编码后的视频/音频数据。它的声明如下：
/*** Read encoded data from the encoder.** @param avctx codec context* @param avpkt This will be set to a reference-counted packet allocated by the* encoder. Note that the function will always call* av_packet_unref(avpkt) before doing anything else.* @return 0 on success, otherwise negative error code:* AVERROR(EAGAIN): output is not available in the current state - user* must try to send input* AVERROR_EOF: the encoder has been fully flushed, and there will be* no more output packets* AVERROR(EINVAL): codec not opened, or it is a decoder* other errors: legitimate encoding errors*/
int avcodec_receive_packet(AVCodecContext *avctx, AVPacket *avpkt);int attribute_align_arg avcodec_receive_packet(AVCodecContext *avctx, AVPacket *avpkt)
{AVCodecInternal *avci = avctx->internal;int ret;av_packet_unref(avpkt);if (!avcodec_is_open(avctx) || !av_codec_is_encoder(avctx->codec))return AVERROR(EINVAL);if (avci->buffer_pkt->data || avci->buffer_pkt->side_data) {av_packet_move_ref(avpkt, avci->buffer_pkt);} else {ret = encode_receive_packet_internal(avctx, avpkt);if (ret < 0)return ret;}return 0;
}
注意事项
- 旧版本视频编码使用 avcodec_encode_video2，音频编码使用 avcodec_encode_audio2；新版本音视频编码统一使用 avcodec_send_frame 和 avcodec_receive_packet
- 旧版本 API 内部直接调用了 AVCodec 的函数指针 encode2；新版本 API 首先会判断编码器是否实现了函数指针 send_frame 和 receive_packet，如果实现了，优先使用send_frame 和 receive_packet，否则使用旧版本的 encode2 未找到代码证明，每个版本之间差异较大
- 目前仅发现编码器 ff_hevc_nvenc_encoder 实现了新版本的 API（send_frame 和 receive_packet），libx264、AAC 等编码器依然使用了旧版本的 API（encode2）
)
)
等）)
)
)
)