介绍

1. FFmpeg 是一个可以处理音视频的软件，功能非常强大，主要包括，编解码转换，封装格式转换，滤镜特效。
2. FFmpeg支持各种网络协议，支持 RTMP ，RTSP，HLS 等高层协议的推拉流，也支持更底层的TCP/UDP 协议推拉流。
3. FFmpeg 可以在 Windows，Linux，Mac，iOS，Android等操作系统上运行。
4. FFmpeg 是 " Fast Forward mpeg " 的缩写；
5. FFMPEG从功能上划分为几个模块，分别为核心工具（libutils）、媒体格式（libavformat）、编解码（libavcodec）、设备（libavdevice）和后处理（libavfilter, libswscale, libpostproc），分别负责提供公用的功能函数、实现多媒体文件的读包和写包、完成音视频的编解码、管理音视频设备的操作以及进行音视频后处理。
6. ffmpeg的可执行文件是 FFmpeg 官方提供的转换工具，是命令行工具，核心代码主要在 ffmpeg.c文件中。

ffmpeg.c函数关系分析总图

关键函数介绍

transcode()

1. 转换的核心功能主要就在 transcode()函数中，此函数中最核心的就是 transcode_step()，该函数完成了音视频的转换的核心能力。
2. 其中 transcode_init()主要完成一些初始化的工作，内部通过init_input_stream()来实现调用 API函数avcodec_open2()完成解码器的打开工作。
   

transcode_step()

1. transcode_step()是完成音视频转码的核心函数，其中 process_input()完成解码功能模块，reap_filter()完成了编码功能模块。
   

process_input()

1. process_input()函数实现了解码功能，其中 process_input_packet()是完成解码的核心函数。
   
2. 在 process_input_packet()中会根据不同的音视频解码需要调用不同的函数，音频调用的就是 decode_audio()，视频调用的是 decode_video()函数，字幕调用的是 transcode_subtitles()函数，如果只是进行 copy 功能，需要调用 do_streamcopy()函数。
   
3. 在decode_video()函数中主要完成了解码和发送 frame 的功能，其中 decode()中调用了 API 函数avcodec_send_packet()、avcodec_receive_frame()两个函数完成音视频多媒体的解码功能模块；send_frame_to_filters()主要是对解码后的帧等送到滤镜中，便于下一步的编码使用。
   

reap_filter()

1. reap_filter()函数实现了编码功能。其中视频编码的核心函数是do_video_out()函数，音频编码的核心函数是 do_audio_out()函数。
   
2. 其中 do_video_out()函数完成是视频的 frame 到 packet 的过程，即编码功能。其中调用了 API 函数avcodec_send_frame()、avcodec_receive_packet()完成编码。而 output_packet()完成了将最后的视频包 packet 输出的功能。
   

官方转码实例

1. 该 example 主要根据新版 API 完成了音视频转码的功能。

/** Copyright (c) 2010 Nicolas George* Copyright (c) 2011 Stefano Sabatini* Copyright (c) 2014 Andrey Utkin** Permission is hereby granted, free of charge, to any person obtaining a copy* of this software and associated documentation files (the "Software"), to deal* in the Software without restriction, including without limitation the rights* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell* copies of the Software, and to permit persons to whom the Software is* furnished to do so, subject to the following conditions:** The above copyright notice and this permission notice shall be included in* all copies or substantial portions of the Software.** THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN* THE SOFTWARE.*//*** @file* API example for demuxing, decoding, filtering, encoding and muxing* @example transcoding.c*/#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavfilter/buffersink.h>
#include <libavfilter/buffersrc.h>
#include <libavutil/opt.h>
#include <libavutil/pixdesc.h>static AVFormatContext *ifmt_ctx;
static AVFormatContext *ofmt_ctx;
typedef struct FilteringContext {AVFilterContext *buffersink_ctx;AVFilterContext *buffersrc_ctx;AVFilterGraph *filter_graph;
} FilteringContext;
static FilteringContext *filter_ctx;typedef struct StreamContext {AVCodecContext *dec_ctx;AVCodecContext *enc_ctx;
} StreamContext;
static StreamContext *stream_ctx;static int open_input_file(const char *filename)
{int ret;unsigned int i;ifmt_ctx = NULL;if ((ret = avformat_open_input(&ifmt_ctx, filename, NULL, NULL)) < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n");return ret;}if ((ret = avformat_find_stream_info(ifmt_ctx, NULL)) < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n");return ret;}stream_ctx = av_mallocz_array(ifmt_ctx->nb_streams, sizeof(*stream_ctx));if (!stream_ctx)return AVERROR(ENOMEM);for (i = 0; i < ifmt_ctx->nb_streams; i++) {AVStream *stream = ifmt_ctx->streams[i];AVCodec *dec = avcodec_find_decoder(stream->codecpar->codec_id);AVCodecContext *codec_ctx;if (!dec) {av_log(NULL, AV_LOG_ERROR, "Failed to find decoder for stream #%u\n", i);return AVERROR_DECODER_NOT_FOUND;}codec_ctx = avcodec_alloc_context3(dec);if (!codec_ctx) {av_log(NULL, AV_LOG_ERROR, "Failed to allocate the decoder context for stream #%u\n", i);return AVERROR(ENOMEM);}ret = avcodec_parameters_to_context(codec_ctx, stream->codecpar);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Failed to copy decoder parameters to input decoder context ""for stream #%u\n", i);return ret;}/* Reencode video & audio and remux subtitles etc. */if (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO|| codec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {if (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO)codec_ctx->framerate = av_guess_frame_rate(ifmt_ctx, stream, NULL);/* Open decoder */ret = avcodec_open2(codec_ctx, dec, NULL);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Failed to open decoder for stream #%u\n", i);return ret;}}stream_ctx[i].dec_ctx = codec_ctx;}av_dump_format(ifmt_ctx, 0, filename, 0);return 0;
}static int open_output_file(const char *filename)
{AVStream *out_stream;AVStream *in_stream;AVCodecContext *dec_ctx, *enc_ctx;AVCodec *encoder;int ret;unsigned int i;ofmt_ctx = NULL;avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, filename);if (!ofmt_ctx) {av_log(NULL, AV_LOG_ERROR, "Could not create output context\n");return AVERROR_UNKNOWN;}for (i = 0; i < ifmt_ctx->nb_streams; i++) {out_stream = avformat_new_stream(ofmt_ctx, NULL);if (!out_stream) {av_log(NULL, AV_LOG_ERROR, "Failed allocating output stream\n");return AVERROR_UNKNOWN;}in_stream = ifmt_ctx->streams[i];dec_ctx = stream_ctx[i].dec_ctx;if (dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO|| dec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {/* in this example, we choose transcoding to same codec */encoder = avcodec_find_encoder(dec_ctx->codec_id);if (!encoder) {av_log(NULL, AV_LOG_FATAL, "Necessary encoder not found\n");return AVERROR_INVALIDDATA;}enc_ctx = avcodec_alloc_context3(encoder);if (!enc_ctx) {av_log(NULL, AV_LOG_FATAL, "Failed to allocate the encoder context\n");return AVERROR(ENOMEM);}/* In this example, we transcode to same properties (picture size,* sample rate etc.). These properties can be changed for output* streams easily using filters */if (dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO) {enc_ctx->height = dec_ctx->height;enc_ctx->width = dec_ctx->width;enc_ctx->sample_aspect_ratio = dec_ctx->sample_aspect_ratio;/* take first format from list of supported formats */if (encoder->pix_fmts)enc_ctx->pix_fmt = encoder->pix_fmts[0];elseenc_ctx->pix_fmt = dec_ctx->pix_fmt;/* video time_base can be set to whatever is handy and supported by encoder */enc_ctx->time_base = av_inv_q(dec_ctx->framerate);} else {enc_ctx->sample_rate = dec_ctx->sample_rate;enc_ctx->channel_layout = dec_ctx->channel_layout;enc_ctx->channels = av_get_channel_layout_nb_channels(enc_ctx->channel_layout);/* take first format from list of supported formats */enc_ctx->sample_fmt = encoder->sample_fmts[0];enc_ctx->time_base = (AVRational){1, enc_ctx->sample_rate};}if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)enc_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;/* Third parameter can be used to pass settings to encoder */ret = avcodec_open2(enc_ctx, encoder, NULL);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot open video encoder for stream #%u\n", i);return ret;}ret = avcodec_parameters_from_context(out_stream->codecpar, enc_ctx);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Failed to copy encoder parameters to output stream #%u\n", i);return ret;}out_stream->time_base = enc_ctx->time_base;stream_ctx[i].enc_ctx = enc_ctx;} else if (dec_ctx->codec_type == AVMEDIA_TYPE_UNKNOWN) {av_log(NULL, AV_LOG_FATAL, "Elementary stream #%d is of unknown type, cannot proceed\n", i);return AVERROR_INVALIDDATA;} else {/* if this stream must be remuxed */ret = avcodec_parameters_copy(out_stream->codecpar, in_stream->codecpar);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Copying parameters for stream #%u failed\n", i);return ret;}out_stream->time_base = in_stream->time_base;}}av_dump_format(ofmt_ctx, 0, filename, 1);if (!(ofmt_ctx->oformat->flags & AVFMT_NOFILE)) {ret = avio_open(&ofmt_ctx->pb, filename, AVIO_FLAG_WRITE);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Could not open output file '%s'", filename);return ret;}}/* init muxer, write output file header */ret = avformat_write_header(ofmt_ctx, NULL);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Error occurred when opening output file\n");return ret;}return 0;
}static int init_filter(FilteringContext* fctx, AVCodecContext *dec_ctx,AVCodecContext *enc_ctx, const char *filter_spec)
{char args[512];int ret = 0;const AVFilter *buffersrc = NULL;const AVFilter *buffersink = NULL;AVFilterContext *buffersrc_ctx = NULL;AVFilterContext *buffersink_ctx = NULL;AVFilterInOut *outputs = avfilter_inout_alloc();AVFilterInOut *inputs  = avfilter_inout_alloc();AVFilterGraph *filter_graph = avfilter_graph_alloc();if (!outputs || !inputs || !filter_graph) {ret = AVERROR(ENOMEM);goto end;}if (dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO) {buffersrc = avfilter_get_by_name("buffer");buffersink = avfilter_get_by_name("buffersink");if (!buffersrc || !buffersink) {av_log(NULL, AV_LOG_ERROR, "filtering source or sink element not found\n");ret = AVERROR_UNKNOWN;goto end;}snprintf(args, sizeof(args),"video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",dec_ctx->width, dec_ctx->height, dec_ctx->pix_fmt,dec_ctx->time_base.num, dec_ctx->time_base.den,dec_ctx->sample_aspect_ratio.num,dec_ctx->sample_aspect_ratio.den);ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",args, NULL, filter_graph);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot create buffer source\n");goto end;}ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",NULL, NULL, filter_graph);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot create buffer sink\n");goto end;}ret = av_opt_set_bin(buffersink_ctx, "pix_fmts",(uint8_t*)&enc_ctx->pix_fmt, sizeof(enc_ctx->pix_fmt),AV_OPT_SEARCH_CHILDREN);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot set output pixel format\n");goto end;}} else if (dec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {buffersrc = avfilter_get_by_name("abuffer");buffersink = avfilter_get_by_name("abuffersink");if (!buffersrc || !buffersink) {av_log(NULL, AV_LOG_ERROR, "filtering source or sink element not found\n");ret = AVERROR_UNKNOWN;goto end;}if (!dec_ctx->channel_layout)dec_ctx->channel_layout =av_get_default_channel_layout(dec_ctx->channels);snprintf(args, sizeof(args),"time_base=%d/%d:sample_rate=%d:sample_fmt=%s:channel_layout=0x%"PRIx64,dec_ctx->time_base.num, dec_ctx->time_base.den, dec_ctx->sample_rate,av_get_sample_fmt_name(dec_ctx->sample_fmt),dec_ctx->channel_layout);ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",args, NULL, filter_graph);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot create audio buffer source\n");goto end;}ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",NULL, NULL, filter_graph);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot create audio buffer sink\n");goto end;}ret = av_opt_set_bin(buffersink_ctx, "sample_fmts",(uint8_t*)&enc_ctx->sample_fmt, sizeof(enc_ctx->sample_fmt),AV_OPT_SEARCH_CHILDREN);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot set output sample format\n");goto end;}ret = av_opt_set_bin(buffersink_ctx, "channel_layouts",(uint8_t*)&enc_ctx->channel_layout,sizeof(enc_ctx->channel_layout), AV_OPT_SEARCH_CHILDREN);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot set output channel layout\n");goto end;}ret = av_opt_set_bin(buffersink_ctx, "sample_rates",(uint8_t*)&enc_ctx->sample_rate, sizeof(enc_ctx->sample_rate),AV_OPT_SEARCH_CHILDREN);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot set output sample rate\n");goto end;}} else {ret = AVERROR_UNKNOWN;goto end;}/* Endpoints for the filter graph. */outputs->name       = av_strdup("in");outputs->filter_ctx = buffersrc_ctx;outputs->pad_idx    = 0;outputs->next       = NULL;inputs->name       = av_strdup("out");inputs->filter_ctx = buffersink_ctx;inputs->pad_idx    = 0;inputs->next       = NULL;if (!outputs->name || !inputs->name) {ret = AVERROR(ENOMEM);goto end;}if ((ret = avfilter_graph_parse_ptr(filter_graph, filter_spec,&inputs, &outputs, NULL)) < 0)goto end;if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)goto end;/* Fill FilteringContext */fctx->buffersrc_ctx = buffersrc_ctx;fctx->buffersink_ctx = buffersink_ctx;fctx->filter_graph = filter_graph;end:avfilter_inout_free(&inputs);avfilter_inout_free(&outputs);return ret;
}static int init_filters(void)
{const char *filter_spec;unsigned int i;int ret;filter_ctx = av_malloc_array(ifmt_ctx->nb_streams, sizeof(*filter_ctx));if (!filter_ctx)return AVERROR(ENOMEM);for (i = 0; i < ifmt_ctx->nb_streams; i++) {filter_ctx[i].buffersrc_ctx  = NULL;filter_ctx[i].buffersink_ctx = NULL;filter_ctx[i].filter_graph   = NULL;if (!(ifmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO|| ifmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO))continue;if (ifmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)filter_spec = "null"; /* passthrough (dummy) filter for video */elsefilter_spec = "anull"; /* passthrough (dummy) filter for audio */ret = init_filter(&filter_ctx[i], stream_ctx[i].dec_ctx,stream_ctx[i].enc_ctx, filter_spec);if (ret)return ret;}return 0;
}static int encode_write_frame(AVFrame *filt_frame, unsigned int stream_index, int *got_frame) {int ret;int got_frame_local;AVPacket enc_pkt;int (*enc_func)(AVCodecContext *, AVPacket *, const AVFrame *, int *) =(ifmt_ctx->streams[stream_index]->codecpar->codec_type ==AVMEDIA_TYPE_VIDEO) ? avcodec_encode_video2 : avcodec_encode_audio2;if (!got_frame)got_frame = &got_frame_local;av_log(NULL, AV_LOG_INFO, "Encoding frame\n");/* encode filtered frame */enc_pkt.data = NULL;enc_pkt.size = 0;av_init_packet(&enc_pkt);ret = enc_func(stream_ctx[stream_index].enc_ctx, &enc_pkt,filt_frame, got_frame);av_frame_free(&filt_frame);if (ret < 0)return ret;if (!(*got_frame))return 0;/* prepare packet for muxing */enc_pkt.stream_index = stream_index;av_packet_rescale_ts(&enc_pkt,stream_ctx[stream_index].enc_ctx->time_base,ofmt_ctx->streams[stream_index]->time_base);av_log(NULL, AV_LOG_DEBUG, "Muxing frame\n");/* mux encoded frame */ret = av_interleaved_write_frame(ofmt_ctx, &enc_pkt);return ret;
}static int filter_encode_write_frame(AVFrame *frame, unsigned int stream_index)
{int ret;AVFrame *filt_frame;av_log(NULL, AV_LOG_INFO, "Pushing decoded frame to filters\n");/* push the decoded frame into the filtergraph */ret = av_buffersrc_add_frame_flags(filter_ctx[stream_index].buffersrc_ctx,frame, 0);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Error while feeding the filtergraph\n");return ret;}/* pull filtered frames from the filtergraph */while (1) {filt_frame = av_frame_alloc();if (!filt_frame) {ret = AVERROR(ENOMEM);break;}av_log(NULL, AV_LOG_INFO, "Pulling filtered frame from filters\n");ret = av_buffersink_get_frame(filter_ctx[stream_index].buffersink_ctx,filt_frame);if (ret < 0) {/* if no more frames for output - returns AVERROR(EAGAIN)* if flushed and no more frames for output - returns AVERROR_EOF* rewrite retcode to 0 to show it as normal procedure completion*/if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)ret = 0;av_frame_free(&filt_frame);break;}filt_frame->pict_type = AV_PICTURE_TYPE_NONE;ret = encode_write_frame(filt_frame, stream_index, NULL);if (ret < 0)break;}return ret;
}static int flush_encoder(unsigned int stream_index)
{int ret;int got_frame;if (!(stream_ctx[stream_index].enc_ctx->codec->capabilities &AV_CODEC_CAP_DELAY))return 0;while (1) {av_log(NULL, AV_LOG_INFO, "Flushing stream #%u encoder\n", stream_index);ret = encode_write_frame(NULL, stream_index, &got_frame);if (ret < 0)break;if (!got_frame)return 0;}return ret;
}int main(int argc, char **argv)
{int ret;AVPacket packet = { .data = NULL, .size = 0 };AVFrame *frame = NULL;enum AVMediaType type;unsigned int stream_index;unsigned int i;int got_frame;int (*dec_func)(AVCodecContext *, AVFrame *, int *, const AVPacket *);if (argc != 3) {av_log(NULL, AV_LOG_ERROR, "Usage: %s <input file> <output file>\n", argv[0]);return 1;}if ((ret = open_input_file(argv[1])) < 0)goto end;if ((ret = open_output_file(argv[2])) < 0)goto end;if ((ret = init_filters()) < 0)goto end;/* read all packets */while (1) {if ((ret = av_read_frame(ifmt_ctx, &packet)) < 0)break;stream_index = packet.stream_index;type = ifmt_ctx->streams[packet.stream_index]->codecpar->codec_type;av_log(NULL, AV_LOG_DEBUG, "Demuxer gave frame of stream_index %u\n",stream_index);if (filter_ctx[stream_index].filter_graph) {av_log(NULL, AV_LOG_DEBUG, "Going to reencode&filter the frame\n");frame = av_frame_alloc();if (!frame) {ret = AVERROR(ENOMEM);break;}av_packet_rescale_ts(&packet,ifmt_ctx->streams[stream_index]->time_base,stream_ctx[stream_index].dec_ctx->time_base);dec_func = (type == AVMEDIA_TYPE_VIDEO) ? avcodec_decode_video2 :avcodec_decode_audio4;ret = dec_func(stream_ctx[stream_index].dec_ctx, frame,&got_frame, &packet);if (ret < 0) {av_frame_free(&frame);av_log(NULL, AV_LOG_ERROR, "Decoding failed\n");break;}if (got_frame) {frame->pts = frame->best_effort_timestamp;ret = filter_encode_write_frame(frame, stream_index);av_frame_free(&frame);if (ret < 0)goto end;} else {av_frame_free(&frame);}} else {/* remux this frame without reencoding */av_packet_rescale_ts(&packet,ifmt_ctx->streams[stream_index]->time_base,ofmt_ctx->streams[stream_index]->time_base);ret = av_interleaved_write_frame(ofmt_ctx, &packet);if (ret < 0)goto end;}av_packet_unref(&packet);}/* flush filters and encoders */for (i = 0; i < ifmt_ctx->nb_streams; i++) {/* flush filter */if (!filter_ctx[i].filter_graph)continue;ret = filter_encode_write_frame(NULL, i);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Flushing filter failed\n");goto end;}/* flush encoder */ret = flush_encoder(i);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Flushing encoder failed\n");goto end;}}av_write_trailer(ofmt_ctx);
end:av_packet_unref(&packet);av_frame_free(&frame);for (i = 0; i < ifmt_ctx->nb_streams; i++) {avcodec_free_context(&stream_ctx[i].dec_ctx);if (ofmt_ctx && ofmt_ctx->nb_streams > i && ofmt_ctx->streams[i] && stream_ctx[i].enc_ctx)avcodec_free_context(&stream_ctx[i].enc_ctx);if (filter_ctx && filter_ctx[i].filter_graph)avfilter_graph_free(&filter_ctx[i].filter_graph);}av_free(filter_ctx);av_free(stream_ctx);avformat_close_input(&ifmt_ctx);if (ofmt_ctx && !(ofmt_ctx->oformat->flags & AVFMT_NOFILE))avio_closep(&ofmt_ctx->pb);avformat_free_context(ofmt_ctx);if (ret < 0)av_log(NULL, AV_LOG_ERROR, "Error occurred: %s\n", av_err2str(ret));return ret ? 1 : 0;
}

参考

1. http://ffmpeg.org/