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• How to change mp4 aspect ratio to 16:9 using ffmpeg ?

  1er mai 2016, par user1788736

  I got an mp4 video that I copy 4 minute of it using ffmpeg. After uploading to YouTube I noticed the uploaded video has black bars on both side of video(right and left side) !After searching for a way to remove those black bars I found that I need to use yt:stretch=16:9 !However,using yt:stretch=16.9 tag will not remove the black bars on iPhone and Samsung smart tv YouTube app !

  could an expert help me change the aspect ratio of original mp4 video to 16:9 using ffmpeg (without losing video quality) for re uploading to YouTube ? Thanks in advance ?

  I got two types of source with following information :

  1)Resolution:720x576 ,Frame rate:25 . Codec:H264 - MPEG-4 AVC(part 10)(avc1),
  
  2)Resolution:848x480 , Frame rate:24.804393,Codec:H264 - MPEG-4 AVC(part 10)(avc1)

  ffmpeg code used to trim the original video :

     ffmpeg -i orginalVideo.mp4 -ss 00:25:55 -t 00:04:02 -acodec copy -vcodec copy videoForYoutube.mp4

• opencv V3 mixing shared and non shared

  31 décembre 2015, par Kellerspeicher

  The current stable (V3.0.0) and unstable (V3.1.0) version of openCV is mixing shared and non shared libraries if compiled on an Ubuntu 14.04.3 LTS.

  Linking CXX shared library ../../lib/libopencv_videoio.so
  
  /usr/bin/ld: /usr/local/lib/libavcodec.a(avpacket.o): relocation R_X86_64_32 against `.rodata.str1.1' can not be used when making a shared object; recompile with -fPIC
  
  /usr/local/lib/libavcodec.a: error adding symbols: Bad value
  
  collect2: error: ld returned 1 exit status
  
  make[2]: *** [lib/libopencv_videoio.so.3.1.0] Error 1
  
  make[1]: *** [modules/videoio/CMakeFiles/opencv_videoio.dir/all] Error 2
  
  make: *** [all] Error 2

  Trying to create libopencv_videoio.so using libavcodec.a seems to be the problem. There is a bug report about that, but it is only giving the advice to check if libavcodec.so is installed (which is) and a workaround to use -DBUILD_SHARED_LIBS=OFF to prevent creation of shared libraries. Does anyone knows the reason for this problem. The openCV people just state the Ubuntu packaged ffmpeg library to be not correct. Any idea ?

  The problem seems to be old. I just found a very similar question not answered but commented with the advice of compiling ffmpeg with ./configure --enable-shared. But there is already a shared library /usr/lib/x86_64-linux-gnu/libavcodec.so which obviously is not found. I am not a cmake expert but couldn’t it be a problem of a miss leaded build process ?

• Encode live audio stream with ffmpeg

  11 novembre 2015, par Victor Canezin de Oliveira

  Someone please help me.

  I’m trying to encode a live audio stream with ffmpeg. I’m using it Chrome’s native client.

  It’s getting the audio from GetUserMedia() and sending it to pnacl. It receives the audio and send it to ffmpeg to encode. The problem is the final audio is chopped.

  I think the problem is that the codec frame_size is larger than the stream nb_samples (1152 and 480 respectively) and it’s leaving a "blank" audio data at the end of each frame (I’m no audio expert).

  I am creating the AVFrame like this :

  AVFrame *frame = av_frame_alloc();
  
  frame->nb_samples = nb_samples; //(I get it from the stream)
  
  AVSampleFormat sample_fmt = ost->st->codec->sample_fmt;
  
  // nb_channels, buffer and buffer_size I get from the stream
  
  
  
  avcodec_fill_audio_frame(frame, nb_channels, sample_fmt, buffer, buffer_size, 0);

  And encoding with avcodec_encode_audio2

  I am using a mix of nacl example and muxing.c example from ffmpeg.

  Can someone help me ?