使用ffmpeg实现转码样例(代码实现)

使用ffmpeg实现转码样例(代码实现)

使用ffmpeg转码主要工作如下:

Demux -> Decoding -> Encoding -> Muxing

其中接口调用如下：

 

    av_register_all();
    avformat_open_input
    avformat_find_stream_info
    open_codec_context
    av_image_alloc
    avcodec_alloc_frame
    avformat_alloc_output_context2
    avcodec_open2
    avcodec_alloc_frame
    avpicture_alloc
    avpicture_alloc
    avformat_write_header
    av_init_packet
    av_read_frame
    avcodec_decode_video2
    av_image_copy
    avcodec_encode_video2
    av_interleaved_write_frame
    av_write_trailer

下面的代码为主要将视频转码，封装为h264编码格式的mp4文件，音频为mp3，但是主要操作并不处理音频文件。代码如下

    #include <stdlib.h>
    #include <stdio.h>
    #include <string.h>
    #include <math.h>

    #include <libavutil/opt.h>
    #include <libavutil/mathematics.h>
    #include <libavformat/avformat.h>
    #include <libswscale/swscale.h>
    #include <libswresample/swresample.h>

    /* 5 seconds stream duration */
    #define STREAM_DURATION 200.0
    #define STREAM_FRAME_RATE 25 /* 25 images/s */
    #define STREAM_NB_FRAMES ((int)(STREAM_DURATION * STREAM_FRAME_RATE))
    #define STREAM_PIX_FMT AV_PIX_FMT_YUV420P /* default pix_fmt */

    static AVFormatContext *input_fmt_ctx = NULL;
    static int sws_flags = SWS_BICUBIC;
    static AVPacket input_pkt;
    static int video_stream_idx = -1;
    static uint8_t *video_dst_data[4] = {NULL};
    static int video_dst_linesize[4];
    static AVStream *input_video_stream;
    static AVFrame *input_frame;
    static AVCodecContext *video_dec_ctx = NULL;
    static int video_dst_bufsize;


    static int open_codec_context(int *stream_idx,
     AVFormatContext *fmt_ctx, enum AVMediaType type)
    {
     int ret;
     AVStream *st;
     AVCodecContext *dec_ctx = NULL;
     AVCodec *dec = NULL;

     ret = av_find_best_stream(fmt_ctx, type, -1, -1, NULL, 0);
     if (ret < 0) {
     return ret;
     } else {
     *stream_idx = ret;
     st = fmt_ctx->streams[*stream_idx];

     /* find decoder for the stream */
     dec_ctx = st->codec;
     dec = avcodec_find_decoder(dec_ctx->codec_id);
     if (!dec) {
     fprintf(stderr, "Failed to find %s codec
",
     av_get_media_type_string(type));
     return ret;
     }

     if ((ret = avcodec_open2(dec_ctx, dec, NULL)) < 0) {
     fprintf(stderr, "Failed to open %s codec
",
     av_get_media_type_string(type));
     return ret;
     }
     }

     return 0;
    }

    /* Add an output stream. */
    static AVStream *add_stream(AVFormatContext *oc, AVCodec **codec,
     enum AVCodecID codec_id)
    {
     AVCodecContext *c;
     AVStream *st;

     /* find the encoder */
     *codec = avcodec_find_encoder(codec_id);
     if (!(*codec)) {
     fprintf(stderr, "Could not find encoder for '%s'
",
     avcodec_get_name(codec_id));
     exit(1);
     }

     st = avformat_new_stream(oc, *codec);
     if (!st) {
     fprintf(stderr, "Could not allocate stream
");
     exit(1);
     }
     st->id = oc->nb_streams-1;
     c = st->codec;

     switch ((*codec)->type) {
     case AVMEDIA_TYPE_AUDIO:
     c->sample_fmt = AV_SAMPLE_FMT_FLTP;
     c->bit_rate = 64000;
     c->sample_rate = 44100;
     c->channels = 2;
     break;

     case AVMEDIA_TYPE_VIDEO:
     c->codec_id = codec_id;

     c->bit_rate = 400000;
     c->time_base.den = STREAM_FRAME_RATE;
     c->time_base.num = 1;
     c->gop_size = 12;
     c->pix_fmt = STREAM_PIX_FMT;
     break;

     default:
     break;
     }

     /* Some formats want stream headers to be separate. */
     if (oc->oformat->flags & AVFMT_GLOBALHEADER)
     c->flags |= CODEC_FLAG_GLOBAL_HEADER;

     return st;
    }

    /**************************************************************/
    /* audio output */

    static float t, tincr, tincr2;

    static uint8_t **src_samples_data;
    static int src_samples_linesize;
    static int src_nb_samples;

    static int max_dst_nb_samples;
    uint8_t **dst_samples_data;
    int dst_samples_linesize;
    int dst_samples_size;

    struct SwrContext *swr_ctx = NULL;

    static void open_audio(AVFormatContext *oc, AVCodec *codec, AVStream *st)
    {
     AVCodecContext *c;
     int ret;

     c = st->codec;

     /* open it */
     ret = avcodec_open2(c, codec, NULL);
     if (ret < 0) {
     fprintf(stderr, "Could not open audio codec: %s
", av_err2str(ret));
     exit(1);
     }

     /* init signal generator */
     t = 0;
     tincr = 2 * M_PI * 110.0 / c->sample_rate;
     /* increment frequency by 110 Hz per second */
     tincr2 = 2 * M_PI * 110.0 / c->sample_rate / c->sample_rate;

     src_nb_samples = c->codec->capabilities & CODEC_CAP_VARIABLE_FRAME_SIZE ?
     10000 : c->frame_size;

     ret = av_samples_alloc_array_and_samples(&src_samples_data, &src_samples_linesize, c->channels,
     src_nb_samples, c->sample_fmt, 0);
     if (ret < 0) {
     fprintf(stderr, "Could not allocate source samples
");
     exit(1);
     }

     /* create resampler context */
     if (c->sample_fmt != AV_SAMPLE_FMT_S16) {
     swr_ctx = swr_alloc();
     if (!swr_ctx) {
     fprintf(stderr, "Could not allocate resampler context
");
     exit(1);
     }

     /* set options */
     av_opt_set_int (swr_ctx, "in_channel_count", c->channels, 0);
     av_opt_set_int (swr_ctx, "in_sample_rate", c->sample_rate, 0);
     av_opt_set_sample_fmt(swr_ctx, "in_sample_fmt", AV_SAMPLE_FMT_S16, 0);
     av_opt_set_int (swr_ctx, "out_channel_count", c->channels, 0);
     av_opt_set_int (swr_ctx, "out_sample_rate", c->sample_rate, 0);
     av_opt_set_sample_fmt(swr_ctx, "out_sample_fmt", c->sample_fmt, 0);

     /* initialize the resampling context */
     if ((ret = swr_init(swr_ctx)) < 0) {
     fprintf(stderr, "Failed to initialize the resampling context
");
     exit(1);
     }
     }

     /* compute the number of converted samples: buffering is avoided
      * ensuring that the output buffer will contain at least all the
      * converted input samples */
     max_dst_nb_samples = src_nb_samples;
     ret = av_samples_alloc_array_and_samples(&dst_samples_data, &dst_samples_linesize, c->channels,
     max_dst_nb_samples, c->sample_fmt, 0);
     if (ret < 0) {
     fprintf(stderr, "Could not allocate destination samples
");
     exit(1);
     }
     dst_samples_size = av_samples_get_buffer_size(NULL, c->channels, max_dst_nb_samples,
     c->sample_fmt, 0);
    }

    /* Prepare a 16 bit dummy audio frame of 'frame_size' samples and
     * 'nb_channels' channels. */
    static void get_audio_frame(int16_t *samples, int frame_size, int nb_channels)
    {
     int j, i, v;
     int16_t *q;

     q = samples;
     for (j = 0; j < frame_size; j++) {
     v = (int)(sin(t) * 10000);
     for (i = 0; i < nb_channels; i++)
     *q++ = v;
     t += tincr;
     tincr += tincr2;
     }
    }

    static void write_audio_frame(AVFormatContext *oc, AVStream *st)
    {
     AVCodecContext *c;
     AVPacket pkt = { 0 }; // data and size must be 0;
     AVFrame *frame = avcodec_alloc_frame();
     int got_packet, ret, dst_nb_samples;

     av_init_packet(&pkt);
     c = st->codec;

     get_audio_frame((int16_t *)src_samples_data[0], src_nb_samples, c->channels);

     /* convert samples from native format to destination codec format, using the resampler */
     if (swr_ctx) {
     /* compute destination number of samples */
     dst_nb_samples = av_rescale_rnd(swr_get_delay(swr_ctx, c->sample_rate) + src_nb_samples,
     c->sample_rate, c->sample_rate, AV_ROUND_UP);
     if (dst_nb_samples > max_dst_nb_samples) {
     av_free(dst_samples_data[0]);
     ret = av_samples_alloc(dst_samples_data, &dst_samples_linesize, c->channels,
     dst_nb_samples, c->sample_fmt, 0);
     if (ret < 0)
     exit(1);
     max_dst_nb_samples = dst_nb_samples;
     dst_samples_size = av_samples_get_buffer_size(NULL, c->channels, dst_nb_samples,
     c->sample_fmt, 0);
     }

     /* convert to destination format */
     ret = swr_convert(swr_ctx,
     dst_samples_data, dst_nb_samples,
     (const uint8_t **)src_samples_data, src_nb_samples);
     if (ret < 0) {
     fprintf(stderr, "Error while converting
");
     exit(1);
     }
     } else {
     dst_samples_data[0] = src_samples_data[0];
     dst_nb_samples = src_nb_samples;
     }

     frame->nb_samples = dst_nb_samples;
     avcodec_fill_audio_frame(frame, c->channels, c->sample_fmt,
     dst_samples_data[0], dst_samples_size, 0);

     ret = avcodec_encode_audio2(c, &pkt, frame, &got_packet);
     if (ret < 0) {
     fprintf(stderr, "Error encoding audio frame: %s
", av_err2str(ret));
     exit(1);
     }

     if (!got_packet)
     return;

     pkt.stream_index = st->index;

     /* Write the compressed frame to the media file. */
     ret = av_interleaved_write_frame(oc, &pkt);
     if (ret != 0) {
     fprintf(stderr, "Error while writing audio frame: %s
",
     av_err2str(ret));
     exit(1);
     }
     avcodec_free_frame(&frame);
    }

    static void close_audio(AVFormatContext *oc, AVStream *st)
    {
     avcodec_close(st->codec);
     av_free(src_samples_data[0]);
     av_free(dst_samples_data[0]);
    }

    /***********************bbs.ChinaFFmpeg.com****孙悟空***********************/
    /* video output */

    static AVFrame *frame;
    static AVPicture src_picture, dst_picture;
    static int frame_count;

    static void open_video(AVFormatContext *oc, AVCodec *codec, AVStream *st)
    {
     int ret;
     AVCodecContext *c = st->codec;

     /* open the codec */
     ret = avcodec_open2(c, codec, NULL);
     if (ret < 0) {
     fprintf(stderr, "Could not open video codec: %s
", av_err2str(ret));
     exit(1);
     }

     /* allocate and init a re-usable frame */
     frame = avcodec_alloc_frame();
     if (!frame) {
     fprintf(stderr, "Could not allocate video frame
");
     exit(1);
     }

     /* Allocate the encoded raw picture. */
     ret = avpicture_alloc(&dst_picture, c->pix_fmt, c->width, c->height);
     if (ret < 0) {
     fprintf(stderr, "Could not allocate picture: %s
", av_err2str(ret));
     exit(1);
     }

     /* If the output format is not YUV420P, then a temporary YUV420P
      * picture is needed too. It is then converted to the required
      * output format. */
     if (c->pix_fmt != AV_PIX_FMT_YUV420P) {
     ret = avpicture_alloc(&src_picture, AV_PIX_FMT_YUV420P, c->width, c->height);
     if (ret < 0) {
     fprintf(stderr, "Could not allocate temporary picture: %s
",
     av_err2str(ret));
     exit(1);
     }
     }

     /* copy data and linesize picture pointers to frame */
     *((AVPicture *)frame) = dst_picture;
    }

    static void write_video_frame(AVFormatContext *oc, AVStream *st)
    {
     int ret;
     static struct SwsContext *sws_ctx;
     AVCodecContext *c = st->codec;

     // fill_yuv_image(&dst_picture, frame_count, c->width, c->height);


     if (oc->oformat->flags & AVFMT_RAWPICTURE) {
     /* Raw video case - directly store the picture in the packet */
     AVPacket pkt;
     av_init_packet(&pkt);

     pkt.flags |= AV_PKT_FLAG_KEY;
     pkt.stream_index = st->index;
     pkt.data = dst_picture.data[0];
     pkt.size = sizeof(AVPicture);

     ret = av_interleaved_write_frame(oc, &pkt);
     } else {
     AVPacket pkt = { 0 };
     int got_packet;
     av_init_packet(&pkt);

     /* encode the image */
     ret = avcodec_encode_video2(c, &pkt, frame, &got_packet);
     if (ret < 0) {
     fprintf(stderr, "Error encoding video frame: %s
", av_err2str(ret));
     exit(1);
     }
     /* If size is zero, it means the image was buffered. */

     if (!ret && got_packet && pkt.size) {
     pkt.stream_index = st->index;

     /* Write the compressed frame to the media file. */
     ret = av_interleaved_write_frame(oc, &pkt);
     } else {
     ret = 0;
     }
     }
     if (ret != 0) {
     fprintf(stderr, "Error while writing video frame: %s
", av_err2str(ret));
     exit(1);
     }
     frame_count++;
    }

    static void close_video(AVFormatContext *oc, AVStream *st)
    {
     avcodec_close(st->codec);
     av_free(src_picture.data[0]);
     av_free(dst_picture.data[0]);
     av_free(frame);
    }

    /**************************************************************/
    /* media file output */

    int main(int argc, char **argv)
    {
     const char *filename;
     const char *input_file;
     AVOutputFormat *fmt;
     AVFormatContext *oc;
     AVStream *audio_st, *video_st;
     AVCodec *audio_codec, *video_codec;
     double audio_time, video_time;
     int ret;
     int decoded;
     int got_frame;

     /* Initialize libavcodec, and register all codecs and formats. */
     av_register_all();

     if (argc != 3) {
     printf("usage: %s output_file inputfile
"
     "API example program to output a media file with libavformat.
"
     "This program generates a synthetic audio and video stream, encodes and
"
     "muxes them into a file named output_file.
"
     "The output format is automatically guessed according to the file extension.
"
     "Raw images can also be output by using '%%d' in the filename.
"
     "
", argv[0]);
     return 1;
     }

     input_file = argv[2];
     filename = argv[1];

     if (avformat_open_input( &input_fmt_ctx, input_file, NULL, NULL) < 0) {
     fprintf(stderr, "Could not open source file %s
", input_file);
     exit(-1);
     }

     /* retrieve stream information */
     if (avformat_find_stream_info(input_fmt_ctx, NULL) < 0) {
     fprintf(stderr, "Could not find stream information
");
     exit(1);
     }

     if (open_codec_context(&video_stream_idx, input_fmt_ctx, AVMEDIA_TYPE_VIDEO) >= 0) {
     input_video_stream = input_fmt_ctx->streams[video_stream_idx];
     video_dec_ctx = input_video_stream->codec;
     ret = av_image_alloc(video_dst_data, video_dst_linesize,
     video_dec_ctx->width, video_dec_ctx->height,
     video_dec_ctx->pix_fmt, 1);
     if (ret < 0) {
     fprintf(stderr, "Could not allocate raw video buffer
");
     }
     video_dst_bufsize = ret;
     }


     input_frame = avcodec_alloc_frame();
     if (!input_frame) {
     fprintf(stderr, "Could not allocate frame
");
     ret = AVERROR(ENOMEM);
     exit(-1);
     }

     /* allocate the output media context */
     avformat_alloc_output_context2(&oc, NULL, NULL, filename);
     if (!oc) {
     printf("Could not deduce output format from file extension: using MPEG.
");
     avformat_alloc_output_context2(&oc, NULL, "mpeg", filename);
     }
     if (!oc) {
     return 1;
     }
     fmt = oc->oformat;

     video_st = NULL;
     audio_st = NULL;

     fmt->video_codec = AV_CODEC_ID_H264;
     if (fmt->video_codec != AV_CODEC_ID_NONE) {
     video_st = add_stream(oc, &video_codec, AV_CODEC_ID_H264);
     }
     if (video_st->codec) {
     video_st->codec->width = video_dec_ctx->width;
     video_st->codec->height = video_dec_ctx->height;
     }
     fmt->audio_codec = AV_CODEC_ID_MP3;
     if (fmt->audio_codec != AV_CODEC_ID_NONE) {
     audio_st = add_stream(oc, &audio_codec, AV_CODEC_ID_MP3);
     }

     /* Now that all the parameters are set, we can open the audio and
      * video codecs and allocate the necessary encode buffers. */
     if (video_st)
     open_video(oc, video_codec, video_st);
     if (audio_st)
     open_audio(oc, audio_codec, audio_st);

     av_dump_format(oc, 0, filename, 1);


     /* open the output file, if needed */
     if (!(fmt->flags & AVFMT_NOFILE)) {
     ret = avio_open(&oc->pb, filename, AVIO_FLAG_WRITE);
     if (ret < 0) {
     fprintf(stderr, "Could not open '%s': %s
", filename,
     av_err2str(ret));
     return 1;
     }
     }

     /* Write the stream header, if any. */
     ret = avformat_write_header(oc, NULL);
     if (ret < 0) {
     fprintf(stderr, "Error occurred when opening output file: %s
",
     av_err2str(ret));
     return 1;
     }

     av_init_packet(&input_pkt);
     input_pkt.data = NULL;
     input_pkt.size = 0;


     if (frame)
     frame->pts = 0;
     for (;;) {
     /* Compute current audio and video time. */
     audio_time = audio_st ? audio_st->pts.val * av_q2d(audio_st->time_base) : 0.0;
     video_time = video_st ? video_st->pts.val * av_q2d(video_st->time_base) : 0.0;

     if ((!audio_st || audio_time >= STREAM_DURATION) &&
     (!video_st || video_time >= STREAM_DURATION))
     break;

     /* write interleaved audio and video frames */
     if (!video_st || (video_st && audio_st && audio_time < video_time)) {
     write_audio_frame(oc, audio_st);
     } else {
     av_read_frame(input_fmt_ctx, &input_pkt);

     decoded = input_pkt.size;
     if (input_pkt.stream_index == video_stream_idx) {
     /* decode video frame */
     ret = avcodec_decode_video2(video_dec_ctx, input_frame, &got_frame, &input_pkt);
     if (ret < 0) {
     fprintf(stderr, "Error decoding video frame
");
     return ret;
     }

     if (got_frame) {
     av_image_copy(&dst_picture, video_dst_linesize,
     (const uint8_t **)(input_frame->data), input_frame->linesize,
     video_dec_ctx->pix_fmt, video_dec_ctx->width, video_dec_ctx->height);
     }
     }

     write_video_frame(oc, video_st);
     frame->pts += av_rescale_q(1, video_st->codec->time_base, video_st->time_base);
     }
     }

     av_write_trailer(oc);

     /* Close each codec. */
     if (video_st)
     close_video(oc, video_st);
     if (audio_st)
     close_audio(oc, audio_st);

     if (!(fmt->flags & AVFMT_NOFILE))
     avio_close(oc->pb);

     avformat_free_context(oc);
     av_free(input_frame);
     av_free(video_dst_data[0]);
     avcodec_close(video_dec_ctx);
     return 0;
    }

以上代码为从dox/example/muxing.c中修改得到

编译命令如下：

gcc -g doc/examples/muxing.c -o muxing -lavcodec -lavdevice -lavfilter -lavformat -lavutil -lswscale -lswresample -lpostproc -lx264 -lmp3lame -lz -liconv -lbz2

执行命令如下：

./muxing output.mp4 ~/Movies/input.avi

执行后效果如下：

查看转码完成后的多媒体文件的信息：

查看转码后的文件的视频: