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：

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 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

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 #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\n",
  av_get_media_type_string(type));
  return ret;
  }

  if ((ret = avcodec_open2(dec_ctx, dec, NULL)) < 0) {
  fprintf(stderr, "Failed to open %s codec\n",
  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'\n",
  avcodec_get_name(codec_id));
  exit(1);
  }

  st = avformat_new_stream(oc, *codec);
  if (!st) {
  fprintf(stderr, "Could not allocate stream\n");
  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\n", 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\n");
  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\n");
  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\n");
  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\n");
  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\n");
  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\n", 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\n",
  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\n", 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\n");
  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\n", 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\n",
  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\n", 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\n", 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\n"
  "API example program to output a media file with libavformat.\n"
  "This program generates a synthetic audio and video stream, encodes and\n"
  "muxes them into a file named output_file.\n"
  "The output format is automatically guessed according to the file extension.\n"
  "Raw images can also be output by using '%%d' in the filename.\n"
  "\n", 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\n", input_file);
  exit(-1);
  }

  /* retrieve stream information */
  if (avformat_find_stream_info(input_fmt_ctx, NULL) < 0) {
  fprintf(stderr, "Could not find stream information\n");
  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\n");
  }
  video_dst_bufsize = ret;
  }


  input_frame = avcodec_alloc_frame();
  if (!input_frame) {
  fprintf(stderr, "Could not allocate frame\n");
  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.\n");
  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\n", 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\n",
  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\n");
  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;
 }

视频帧计算pts,音频帧没有计算，很奇怪，不知道为什么？frame->pts += av_rescale_q(1, video_st->codec->time_base, video_st->time_base);

以上代码为从dox/example/muxing.c中修改得到

编译命令如下：

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 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：

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 ./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: