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• Mux Audio and Video in C#

  8 mars 2014, par nestedforloop

  I'm looking for a way to join separate audio and video streams into a single container.

  Specifically I have VP8 video (webm container) and 16-bit PCM audio (wav container), which I'd like to combine into a Matroska container.

  So far I can achieve this by saving the streams to files, and calling ffmpeg.exe by using the Process API which produces the result I need, but I'd prefer a solution that doesn't rely on saving the intermediate files to disk or requiring the ffmpeg.exe to be on the server. Any help much appreciated !

• How can i mux H264 stream into MP4 file via libavformat

  6 janvier 2013, par Brian

  I want to realize an application that firstly decode a multi-media file(such as test.mp4 file, video codec id is H264), get a video stream and an audio stream, then make some different in the audio stream, at last encode the video stream(use libx264) and audio stream into a result file(result.mp4). To promote the efficiency, i omitted the decode and encode of video stream, i get the video packet via function "av_read_frame", then output it directly into the result file via function "av_write_frame". But there is no picture in the output file, and the size of output file is fairly small.

  I tracked the ffmpeg code and found that in the function "av_write_frame->mov_write_packet->ff_mov_write_packet", it will call function "ff_avc_parse_nal_units" to obtain the size of nal unit, but the return value is very small(such as 208 bytes).

  I find that the H264 stream in the MP4 file is not stored in Annex-B format, so it can't find start code(0x000001）， now my problem is how can I change the H264 stream to Annex-B format, and make it work ?
  I added start code at the beginning of every frame manually, but it still not work.

  Anyone can give me any hint ?Thanks very much.
  Following is the codes similar with my :

      // write the stream header, if any
  
      av_write_header(pFormatCtxEnc);
  
  
  
      .........
  
      /**
  
      * Init of Encoder and Decoder
  
      */
  
  
  
      bool KeyFlag = false;
  
      bool KeyFlagEx = false;
  
      // Read frames and save frames to disk
  
      int iPts = 1;
  
      av_init_packet(&packet);
  
      while(av_read_frame(pFormatCtxDec, &packet)>=0)
  
      {
  
              if (packet.flags == 1)
  
                      KeyFlag = true;
  
  
  
              if (!KeyFlag)
  
                      continue;
  
  
  
              if (m_bStop)
  
              {
  
                      break;
  
              }
  
  
  
              // Is this a packet from the video stream?
  
              if(packet.stream_index == videoStream)
  
              {
  
                      currentframeNum ++;
  
                      if (progressCB != NULL && currentframeNum%20 == 0)
  
                      {
  
                              float fpercent = (float)currentframeNum/frameNum;
  
                              progressCB(fpercent,m_pUser);
  
                      }
  
  
  
                      if (currentframeNum >= beginFrame && currentframeNum <= endFrane)
  
                      {
  
                              if (packet.flags == 1)
  
                                      KeyFlagEx = true;
  
  
  
                              if (!KeyFlagEx)
  
                                      continue;
  
                              packet.dts = iPts ++;
  
                              av_write_frame(pFormatCtxEnc, &packet);
  
  
  
                      }
  
              }
  
              // Free the packet that was allocated by av_read_frame
  
      }
  
  
  
      // write the trailer, if any
  
      av_write_trailer(pFormatCtxEnc);
  
  
  
      /**
  
      * Release of encoder and decoder
  
      */
  
  
  
      return true;

• PHP and FFMPEG - Performing intelligent video conversion

  24 décembre 2012, par Andrew

  I have an oddly difficult task to perform. I thought it would be easy, but all my efforts have been fruitless.

  I'm converting videos uploaded to a php script from various formats (.avi, .mpg, .wmv, .mov, etc.) to a single .flv format. The conversion is working great but what I'm having trouble with is the resolution of the videos.

  This is the command I'm currently running (with PHP vars) :

  ffmpeg -i $original -ab 96k -b 700k -ar 44100 -s 640x480 -acodec mp3 $converted

  Both $original and $converted contain the full paths to those files. My problem is that this always converts to 640x480 (like I'm telling it to) even when the source is smaller. Obviously, this is a waste of disk space and bandwidth when the video is downloaded. Also, this doesn't account for input videos being in any aspect ratio other than 4:3, resulting in a "squished" conversion if I upload a 16:9 video.

  There are 3 things I need to do :

  1. Determine the aspect ratio of the original video.
  2. If not 4:3, pad top and bottom with black bars.
  3. Convert to 640x480 if either dimension of the original is larger or a 4:3 aspect ratio relating to the width/height of the original (whichever is closer to 640x480).

  I've run ffmpeg -i on a few videos, but I don't see a consistent format or location to find the original's resolution from. Once I'm able to figure that out, I know I can "do the math" to figure out the right size and specify padding to fix the aspect ratio with -padttop, -padbottom, etc.