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• Merge remote-tracking branch ’cehoyos/master’

  4 septembre 2013, par Michael Niedermayer

  Merge remote-tracking branch ’cehoyos/master’
  * cehoyos/master :
  
    Show subtitle resolution in avcodec_string().
  Merged-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/utils.c

• YouTube's HD Video Streaming Server Technology ?

  30 septembre 2013, par bgentry

  Lately I've been researching different methods for streaming MP4s to the browser. Flash Media Server is an obvious choice here (using Cloudfront), and most solutions I've seen use the RTMP protocol.

  However, I spent some time on YouTube with Firebug and Chrome debugger figuring out how their streaming worked and I discovered some interesting differences between some of their videos and quality rates.

  My two sample videos are A and B. A is available up to 480p and B is available up to 1080p. For both videos, all rates up to 480p are served in an FLV container with H.264 video and AAC audio, over HTTP. What's interesting here is that if you have not yet downloaded (cached) the entire video, and you try to skip forward to an uncached part of the video, a new request will be made with a 'begin' parameter equal to the target offset in milliseconds. Example from Video A at 480p :

  http://v11.lscache8.c.youtube.com/videoplayback?ip=0.0.0.0&sparams=id%2Cexpire%2Cip%2Cipbits%2Citag%2Calgorithm%2Cburst%2Cfactor%2Coc%3AU0dWTldQVF9FSkNNNl9PSlhJ&fexp=904806%2C902906%2C903711&algorithm=throttle-factor&itag=35&ipbits=0&burst=40&sver=3&expire=1279756800&key=yt1&signature=D2D704D63C242CF187CAA5B5D5BAFB8DFACAC5FF.39180C01559C976717B651A7EB1D0C6249231EB7&factor=1.25&id=8568eb3135971f6f&begin=111863
  
  
  
  Response Headers:
  
  Cache-Control:public,max-age=23472
  
  Connection:close
  
  Content-Length:14320637
  
  Content-Type:video/x-flv
  
  Date:Wed, 21 Jul 2010 17:23:48 GMT
  
  Expires:Wed, 21 Jul 2010 23:55:00 GMT
  
  Last-Modified:Wed, 19 May 2010 12:31:41 GMT
  
  Server:gvs 1.0
  
  X-Content-Type-Options:nosniff

  The file returned by this URL is a fully valid FLV containing only the portion of the video after the requested offset.

  I did the same kind of test on the higher resolution versions of Video B. At 720p and 1080p, YouTube will return a video in an MP4 container, also with H.264 video and AAC audio. What's impressive to me is that their server takes the same type of offset for an MP4 video (via the 'begin' parameter) and returns a valid, streamable MP4 (moov atom at the front of the file with correct offsets) that also only includes the requested portion of the video.

  So, how does YouTube do this ? How do they generate the FLV or MP4 container on the fly with the correct headers and only the desired segment of the requested video ? I know this can be accomplished using FFMPEG to seek to the desired start point and the qt-faststart script to reposition the moov atom to the front of the stream, but it seems like this would be too slow to handle on-demand for millions of YouTube viewers.

  Ideas ?

  Thanks in advance !

  Footnote : I am not allowed to include more than 1 link at this point, so here is Video A's URL : http:// www.youtube .com/watch ?v=hWjrMTWXH28 "Video available up to 480p"

• How to encode using the FFMpeg in Android (using H263)

  3 juillet 2012, par Kenny910

  I am trying to follow the sample code on encoding in the ffmpeg document and successfully build a application to encode and generate a mp4 file but I face the following problems :

  1) I am using the H263 for encoding but I can only set the width and height of the AVCodecContext to 176x144, for other case (like 720x480 or 640x480) it will return fail.

  2) I can't play the output mp4 file by using the default Android player, isn't it support H263 mp4 file ? p.s. I can play it by using other player

  3) Is there any sample code on encoding other video frame to make a new video (which mean decode the video and encode it back in different quality setting, also i would like to modify the frame content) ?

  Here is my code, thanks !

  JNIEXPORT jint JNICALL Java_com_ffmpeg_encoder_FFEncoder_nativeEncoder(JNIEnv* env, jobject thiz, jstring filename){
  
  
  
  LOGI("nativeEncoder()");
  
  
  
  avcodec_register_all();
  
  avcodec_init();
  
  av_register_all();
  
  
  
  AVCodec         *codec;
  
  AVCodecContext  *codecCtx;
  
  int             i;
  
  int             out_size;
  
  int             size;
  
  int             x;
  
  int             y;
  
  int             output_buffer_size;
  
  FILE            *file;
  
  AVFrame         *picture;
  
  uint8_t         *output_buffer;
  
  uint8_t         *picture_buffer;
  
  
  
  /* Manual Variables */
  
  int             l;
  
  int             fps = 30;
  
  int             videoLength = 5;
  
  
  
  /* find the H263 video encoder */
  
  codec = avcodec_find_encoder(CODEC_ID_H263);
  
  if (!codec) {
  
      LOGI("avcodec_find_encoder() run fail.");
  
  }
  
  
  
  codecCtx = avcodec_alloc_context();
  
  picture = avcodec_alloc_frame();
  
  
  
  /* put sample parameters */
  
  codecCtx->bit_rate = 400000;
  
  /* resolution must be a multiple of two */
  
  codecCtx->width = 176;
  
  codecCtx->height = 144;
  
  /* frames per second */
  
  codecCtx->time_base = (AVRational){1,fps};
  
  codecCtx->pix_fmt = PIX_FMT_YUV420P;
  
  codecCtx->codec_id = CODEC_ID_H263;
  
  codecCtx->codec_type = AVMEDIA_TYPE_VIDEO;
  
  
  
  /* open it */
  
  if (avcodec_open(codecCtx, codec) < 0) {
  
      LOGI("avcodec_open() run fail.");
  
  }
  
  
  
  const char* mfileName = (*env)->GetStringUTFChars(env, filename, 0);
  
  
  
  file = fopen(mfileName, "wb");
  
  if (!file) {
  
      LOGI("fopen() run fail.");
  
  }
  
  
  
  (*env)->ReleaseStringUTFChars(env, filename, mfileName);
  
  
  
  /* alloc image and output buffer */
  
  output_buffer_size = 100000;
  
  output_buffer = malloc(output_buffer_size);
  
  
  
  size = codecCtx->width * codecCtx->height;
  
  picture_buffer = malloc((size * 3) / 2); /* size for YUV 420 */
  
  
  
  picture->data[0] = picture_buffer;
  
  picture->data[1] = picture->data[0] + size;
  
  picture->data[2] = picture->data[1] + size / 4;
  
  picture->linesize[0] = codecCtx->width;
  
  picture->linesize[1] = codecCtx->width / 2;
  
  picture->linesize[2] = codecCtx->width / 2;
  
  
  
  for(l=0;l/encode 1 second of video
  
      for(i=0;i/prepare a dummy image YCbCr
  
          //Y
  
          for(y=0;yheight;y++) {
  
              for(x=0;xwidth;x++) {
  
                  picture->data[0][y * picture->linesize[0] + x] = x + y + i * 3;
  
              }
  
          }
  
  
  
          //Cb and Cr
  
          for(y=0;yheight/2;y++) {
  
              for(x=0;xwidth/2;x++) {
  
                  picture->data[1][y * picture->linesize[1] + x] = 128 + y + i * 2;
  
                  picture->data[2][y * picture->linesize[2] + x] = 64 + x + i * 5;
  
              }
  
          }
  
  
  
          //encode the image
  
          out_size = avcodec_encode_video(codecCtx, output_buffer, output_buffer_size, picture);
  
          fwrite(output_buffer, 1, out_size, file);
  
      }
  
  
  
      //get the delayed frames
  
      for(; out_size; i++) {
  
          out_size = avcodec_encode_video(codecCtx, output_buffer, output_buffer_size, NULL);
  
          fwrite(output_buffer, 1, out_size, file);
  
      }
  
  }
  
  
  
  //add sequence end code to have a real mpeg file
  
  output_buffer[0] = 0x00;
  
  output_buffer[1] = 0x00;
  
  output_buffer[2] = 0x01;
  
  output_buffer[3] = 0xb7;
  
  
  
  fwrite(output_buffer, 1, 4, file);
  
  fclose(file);
  
  free(picture_buffer);
  
  free(output_buffer);
  
  avcodec_close(codecCtx);
  
  av_free(codecCtx);
  
  av_free(picture);
  
  
  
  LOGI("finish");
  
  
  
  return 0; }