transcode.c

#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavfilter/buffersink.h>
#include <libavfilter/buffersrc.h>
#include <libavutil/channel_layout.h>
#include <libavutil/opt.h>
#include <libavutil/pixdesc.h>

// 输入格式上下文
static AVFormatContext *ifmt_ctx;
// 输出格式上下文
static AVFormatContext *ofmt_ctx;

// 滤镜上下文结构体
typedef struct FilteringContext {
    AVFilterContext *buffersink_ctx;
    AVFilterContext *buffersrc_ctx;
    AVFilterGraph *filter_graph;

    // 编码数据包
    AVPacket *enc_pkt;
    // 经过滤镜处理后的帧数据
    AVFrame *filtered_frame;
} FilteringContext;

// 滤镜上下文指针
static FilteringContext *filter_ctx;

// 流上下文结构体
typedef struct StreamContext {
    AVCodecContext *dec_ctx;
    AVCodecContext *enc_ctx;
    
    // 解码帧数据
    AVFrame *dec_frame;
} StreamContext;

// 流上下文指针
static StreamContext *stream_ctx;

// 打开输入文件
static int open_input_file(const char *filename)
{
    int ret;
    unsigned int i;

    // 初始化输入格式上下文
    ifmt_ctx = NULL;
    // 打开输入文件
    if ((ret = avformat_open_input(&ifmt_ctx, filename, NULL, NULL)) < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n");
        return ret;
    }

    // 查找流信息
    if ((ret = avformat_find_stream_info(ifmt_ctx, NULL)) < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n");
        return ret;
    }

    // 分配流上下文数组
    stream_ctx = av_calloc(ifmt_ctx->nb_streams, sizeof(*stream_ctx));
    if (!stream_ctx)
        return AVERROR(ENOMEM);

    // 遍历流
    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        AVStream *stream = ifmt_ctx->streams[i];
        const AVCodec *dec = avcodec_find_decoder(stream->codecpar->codec_id);
        AVCodecContext *codec_ctx;
        // 查找解码器
        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);
        }

        // 复制解码器参数到解码器上下文
        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;
        }

        // 通知解码器数据包时间基准
        // 这是强烈建议，但不是强制性的
        codec_ctx->pkt_timebase = stream->time_base;

        // 重新编码视频和音频，混流字幕等
        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);
            
            // 打开解码器
            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;

        // 分配解码帧内存
        stream_ctx[i].dec_frame = av_frame_alloc();
        if (!stream_ctx[i].dec_frame)
            return AVERROR(ENOMEM);
    }

    // 打印输入文件信息
    av_dump_format(ifmt_ctx, 0, filename, 0);
    return 0;
}

// 打开输出文件
static int open_output_file(const char *filename)
{
    AVStream *out_stream;
    AVStream *in_stream;
    AVCodecContext *dec_ctx, *enc_ctx;
    const AVCodec *encoder;
    int ret;
    unsigned int i;

    // 分配输出格式上下文
    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;
    }

    // 遍历输入流
    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        // 创建输出流
        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) {
            // 选择相同的编解码器进行转码
            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);
            }

            // 设置输出流的属性与输入流相同
            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;
                // 从支持的格式列表中选择第一种格式
                if (encoder->pix_fmts)
                    enc_ctx->pix_fmt = encoder->pix_fmts[0];
                else
                    enc_ctx->pix_fmt = dec_ctx->pix_fmt;
                // 视频时间基准可以设置为任何方便和支持的编码器
                enc_ctx->time_base = av_inv_q(dec_ctx->framerate);
            } else {
                enc_ctx->sample_rate = dec_ctx->sample_rate;
                ret = av_channel_layout_copy(&enc_ctx->channel_layout, &dec_ctx->channel_layout);
                if (ret < 0)
                    return ret;
                // 从支持的格式列表中获取第一种格式
                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;

            // 打开编码器
            ret = avcodec_open2(enc_ctx, encoder, NULL);
            if (ret < 0) {
                av_log(NULL, AV_LOG_ERROR, "Cannot open %s encoder for stream #%u\n", encoder->name, i);
                return ret;
            }

            // 复制解码器参数到输出流
            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 {
            // 如果流需要重新复用
            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;
        }

    }

    // 打印输出文件信息
    av_dump_format(ofmt_ctx, 0, filename, 1);

    // 如果需要，打开输出文件
    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;
        }
    }

    // 初始化混流器并写入文件头部
    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;
    }

    // 视频类型
    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;
        }

        // 设置视频的参数
        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->pkt_timebase.num, dec_ctx->pkt_timebase.den,
                dec_ctx->sample_aspect_ratio.num,
                dec_ctx->sample_aspect_ratio.den);

        // 创建buffer source过滤器
        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;
        }

        // 创建buffer sink过滤器
        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;
        }

        // 设置输出像素格式
        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;
        }
    }
    // 音频类型 
    else if (dec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {
        char buf[64];
        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;
        }

        // 设置音频的参数
        if (dec_ctx->channel_layout.order == AV_CHANNEL_ORDER_UNSPEC)
            av_channel_layout_default(&dec_ctx->channel_layout, dec_ctx->channel_layout.nb_channels);
        av_channel_layout_describe(&dec_ctx->channel_layout, buf, sizeof(buf));
        snprintf(args, sizeof(args),
                "time_base=%d/%d:sample_rate=%d:sample_fmt=%s:channel_layout=%s",
                dec_ctx->pkt_timebase.num, dec_ctx->pkt_timebase.den, dec_ctx->sample_rate,
                av_get_sample_fmt_name(dec_ctx->sample_fmt),
                buf);
        
        // 创建audio buffer source过滤器
        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;
        }

        // 创建audio buffer sink过滤器
        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;
        }

        // 设置输出采样格式
        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;
        }

        // 设置输出声道布局
        av_channel_layout_describe(&enc_ctx->channel_layout, buf, sizeof(buf));
        ret = av_opt_set(buffersink_ctx, "channel_layouts",
                         buf, AV_OPT_SEARCH_CHILDREN);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Cannot set output channel layout\n");
            goto end;
        }

        // 设置输出采样率
        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;
    }

    // 设置过滤器图的输出端点
    outputs->name       = av_strdup("in");
    outputs->filter_ctx = buffersrc_ctx;
    outputs->pad_idx    = 0;
    outputs->next       = NULL;

    // 设置过滤器图的输入端点
    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;
    }

    // 解析过滤器图
    if ((ret = avfilter_graph_parse_ptr(filter_graph, filter_spec,
                    &inputs, &outputs, NULL)) < 0)
        goto end;

    // 配置过滤器图
    if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)
        goto end;

    // 填充FileteringContext结构体
    fctx->buffersrc_ctx = buffersrc_ctx;
    fctx->buffersink_ctx = buffersink_ctx;
    fctx->filter_graph = filter_graph;

end:
    // 释放输入和输出端点
    avfilter_inout_free(&inputs);
    avfilter_inout_free(&outputs);

    return ret;
}

// 初始化滤波器
static int init_filters(void)
{
    // 滤波器规格
    const char *filter_spec;
    unsigned int i;
    int ret;
    // 分配滤波器上下文数组
    filter_ctx = av_malloc_array(ifmt_ctx->nb_streams, sizeof(*filter_ctx));
    if (!filter_ctx)
        return AVERROR(ENOMEM);// 内存分配失败

    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        // 输入buffer上下文
        filter_ctx[i].buffersrc_ctx  = NULL;
        // 输出buffer上下文
        filter_ctx[i].buffersink_ctx = NULL;
        // 滤波器
        filter_ctx[i].filter_graph   = NULL;
        // 不是音频或视频流，跳过
        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"; // 视频流的滤波器规格为视频直播（视频直通）
        else
            filter_spec = "anull"; // 音频流的滤波器规格为anull（音频直通）
        ret = init_filter(&filter_ctx[i], stream_ctx[i].dec_ctx,
                stream_ctx[i].enc_ctx, filter_spec); // 初始化滤波器
        if (ret)
            return ret; // 初始化滤波器失败

        // 分配编码后的数据包
        filter_ctx[i].enc_pkt = av_packet_alloc();
        if (!filter_ctx[i].enc_pkt)
            return AVERROR(ENOMEM); // 内存分配失败

        // 分配滤波后的帧
        filter_ctx[i].filtered_frame = av_frame_alloc();
        if (!filter_ctx[i].filtered_frame)
            return AVERROR(ENOMEM); // 内存分配失败
    }
    // 初始化滤波器成功
    return 0;
}

// 编码和写入帧
static int encode_write_frame(unsigned int stream_index, int flush)
{
    StreamContext *stream = &stream_ctx[stream_index];
    FilteringContext *filter = &filter_ctx[stream_index];
    AVFrame *filt_frame = flush ? NULL : filter->filtered_frame;
    AVPacket *enc_pkt = filter->enc_pkt;
    int ret;

    av_log(NULL, AV_LOG_INFO, "Encoding frame\n");
    // 编码帧
    av_packet_unref(enc_pkt);

    if (filt_frame && filt_frame->pts != AV_NOPTS_VALUE)
        filt_frame->pts = av_rescale_q(filt_frame->pts, filt_frame->time_base,
                                       stream->enc_ctx->time_base);

    ret = avcodec_send_frame(stream->enc_ctx, filt_frame);

    if (ret < 0)
        return ret;

    while (ret >= 0) {
        ret = avcodec_receive_packet(stream->enc_ctx, enc_pkt);

        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
            return 0;

        // 准备封装用的包
        enc_pkt->stream_index = stream_index;
        av_packet_rescale_ts(enc_pkt,
                             stream->enc_ctx->time_base,
                             ofmt_ctx->streams[stream_index]->time_base);

        av_log(NULL, AV_LOG_DEBUG, "Muxing frame\n");
        // 封装编码后的帧
        ret = av_interleaved_write_frame(ofmt_ctx, enc_pkt);
    }

    return ret;
}

// 将解码后的帧经过滤波器图进行滤波、编码和写入
static int filter_encode_write_frame(AVFrame *frame, unsigned int stream_index)
{
    FilteringContext *filter = &filter_ctx[stream_index];
    int ret;

    av_log(NULL, AV_LOG_INFO, "Pushing decoded frame to filters\n");
    // 将解码后的帧推送到滤波器图中
    ret = av_buffersrc_add_frame_flags(filter->buffersrc_ctx,
            frame, 0);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "Error while feeding the filtergraph\n");
        return ret;
    }

    // 从滤波器图中获取滤波后的帧
    while (1) {
        av_log(NULL, AV_LOG_INFO, "Pulling filtered frame from filters\n");
        ret = av_buffersink_get_frame(filter->buffersink_ctx,
                                      filter->filtered_frame);
        if (ret < 0) {
            /* 如果没有更多的输出帧，返回AVERROR(EAGAIN)
             * 如果刷新并且没有更多的输出帧，返回AVERROR_EOF
             * 将返回值重写为0以显示正常的过程完成
             */
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                ret = 0;
            break;
        }

        filter->filtered_frame->time_base = av_buffersink_get_time_base(filter->buffersink_ctx);;
        filter->filtered_frame->pict_type = AV_PICTURE_TYPE_NONE;
        ret = encode_write_frame(stream_index, 0);
        av_frame_unref(filter->filtered_frame);
        if (ret < 0)
            break;
    }

    return ret;
}

// 用于刷新编码器并写入剩余帧
static int flush_encoder(unsigned int stream_index)
{   
    // 检查编码器是否支持延迟编码
    if (!(stream_ctx[stream_index].enc_ctx->codec->capabilities &
                AV_CODEC_CAP_DELAY))
        return 0;

    av_log(NULL, AV_LOG_INFO, "Flushing stream #%u encoder\n", stream_index);
    // 调用encode_write_frame函数刷新编码器并写入剩余的帧
    return encode_write_frame(stream_index, 1);
}

int main(int argc, char **argv)
{
    int ret;
    AVPacket *packet = NULL;
    unsigned int stream_index;
    unsigned int i;

    // 检查命令行参数
    if (argc != 3) {
        av_log(NULL, AV_LOG_ERROR, "Usage: %s <input file> <output file>\n", argv[0]);
        return 1;
    }

    // 打开输入文件
    if ((ret = open_input_file(argv[1])) < 0)
        goto end;
    // 打开输出文件
    if ((ret = open_output_file(argv[2])) < 0)
        goto end;
    // 初始化滤镜
    if ((ret = init_filters()) < 0)
        goto end;
    // 分配AVPacket结构体
    if (!(packet = av_packet_alloc()))
        goto end;

    // 读取所有的包
    while (1) {
        // 从输入文件中读取数据包
        if ((ret = av_read_frame(ifmt_ctx, packet)) < 0)
            break;
        // 获取流索引
        stream_index = packet->stream_index;
        av_log(NULL, AV_LOG_DEBUG, "Demuxer gave frame of stream_index %u\n",
                stream_index);

        // 检查是是否存在滤镜图
        if (filter_ctx[stream_index].filter_graph) {
            StreamContext *stream = &stream_ctx[stream_index];

            av_log(NULL, AV_LOG_DEBUG, "Going to reencode&filter the frame\n");

            // 发送数据包解码器
            ret = avcodec_send_packet(stream->dec_ctx, packet);
            if (ret < 0) {
                av_log(NULL, AV_LOG_ERROR, "Decoding failed\n");
                break;
            }

            // 接收解码后的帧并进行滤镜处理、编码和写入输出文件
            while (ret >= 0) {
                // 接收解码后的帧
                ret = avcodec_receive_frame(stream->dec_ctx, stream->dec_frame);
                if (ret == AVERROR_EOF || ret == AVERROR(EAGAIN))
                    break;
                else if (ret < 0)
                    goto end;
                
                // 设置解码帧的现实时间戳
                stream->dec_frame->pts = stream->dec_frame->best_effort_timestamp;
                // 将解码帧经过滤镜处理、编码并写入输出文件
                ret = filter_encode_write_frame(stream->dec_frame, stream_index);
                if (ret < 0)
                    goto end;
            }
        } else {
            // 无需重新编码的情况下重新复用该帧
            // 重新计算时间戳
            av_packet_rescale_ts(packet,
                                 ifmt_ctx->streams[stream_index]->time_base,
                                 ofmt_ctx->streams[stream_index]->time_base);

            // 将帧写入输出文件
            ret = av_interleaved_write_frame(ofmt_ctx, packet);
            if (ret < 0)
                goto end;
        }
        // 释放数据包
        av_packet_unref(packet);
    }

    // 刷新解码器、滤镜和编码器
    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        StreamContext *stream;

        // 检查是否存在滤镜图
        if (!filter_ctx[i].filter_graph)
            continue;

        stream = &stream_ctx[i];

        av_log(NULL, AV_LOG_INFO, "Flushing stream %u decoder\n", i);

        // 刷新解码器
        ret = avcodec_send_packet(stream->dec_ctx, NULL);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Flushing decoding failed\n");
            goto end;
        }

        while (ret >= 0) {
            // 接收解码后的帧
            ret = avcodec_receive_frame(stream->dec_ctx, stream->dec_frame);
            if (ret == AVERROR_EOF)
                break;
            else if (ret < 0)
                goto end;
            
            // 设置解码帧的现实时间戳
            stream->dec_frame->pts = stream->dec_frame->best_effort_timestamp;
            // 将解码帧经过滤镜处理、编码并写入输出文件
            ret = filter_encode_write_frame(stream->dec_frame, i);
            if (ret < 0)
                goto end;
        }

        // 刷新滤镜
        ret = filter_encode_write_frame(NULL, i);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Flushing filter failed\n");
            goto end;
        }

        // 刷新编码器
        ret = flush_encoder(i);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Flushing encoder failed\n");
            goto end;
        }
    }

    // 写入输出文件尾部信息
    av_write_trailer(ofmt_ctx);
end:    
    // 释放数据包
    av_packet_free(&packet);
    // 释放解码器和编码器的上下文
    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_packet_free(&filter_ctx[i].enc_pkt);
            av_frame_free(&filter_ctx[i].filtered_frame);
        }

        // 释放解码帧
        av_frame_free(&stream_ctx[i].dec_frame);
    } 
    // 释放滤镜上下文和流上下文
    av_free(filter_ctx);
    av_free(stream_ctx);
    // 关闭输入文件
    avformat_close_input(&ifmt_ctx);
    if (ofmt_ctx && !(ofmt_ctx->oformat->flags & AVFMT_NOFILE))
        avio_closep(&ofmt_ctx->pb);
    // 释放输出文件上下文
    avformat_free_context(ofmt_ctx);

    // 打印错误信息（如果有）
    if (ret < 0)
        av_log(NULL, AV_LOG_ERROR, "Error occurred: %s\n", av_err2str(ret));
    
    // 返回程序的退出码
    return ret ? 1 : 0;
}