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• During transcoding, does output quality of a video improve when i give output bitrate more than input video's bitrate ?

  19 septembre 2013, par Jobin Jose

  I use ffmpeg for converting videos.
  As i understand, the bitrate of a video stream is the number of bits which constitute the video over 1 second of time.
  What happens when i specify the output video bitrate to be more than the input video's bitrate ?
  For example :
  If bitrate of "Input.mp4" is 2000KBps and i want to convert it to "Output.mp4" with output bitrate set to 3000KBps.
  How will the converter create the extra 1000 bits(3000-2000) for every second of video ?

• How to capture camera devices on Windows using Libav ?

  22 septembre 2011, par Occulta

  Is there any way to capture frames from as many camera types as DirectShow do on Windows platform using Libav ? I need to capture a camera output without using DirectShow filters and I want my application to work with many camera devices types.

  I have searched the Internet about this capability of libav and found that it can be done via libav using special input format "vfwcap". Something like that (don't sure about code correctness - I wrote it by myself) :

  AVFormatParameters formatParams = NULL;
  
  AVInputFormat* pInfmt = NULL;
  
  pInFormatCtx*  pInFormatCtx = NULL;
  
  
  
  av_register_all();
  
  
  
  //formatParams.device = NULL; //this was probably deprecated and then removed
  
  formatParams.channel = 0;
  
  formatParams.standard = "ntsc"; //deprecated too but still available
  
  formatParams.width = 640;
  
  formatParams.height = 480;
  
  formatParams.time_base.num = 1000;
  
  formatParams.time_base.den = 30000; //so we want 30000/1000 = 30 frames per second
  
  formatParams.prealloced_context = 0;
  
  
  
  
  
  pInfmt = av_find_input_format("vfwcap");
  
  if( !pInfmt )
  
  {
  
    fprintf(stderr,"Unknown input format\n");
  
    return -1;
  
  }
  
  
  
  // Open video file (formatParams can be NULL for autodetecting probably)
  
  if (av_open_input_file(&pInFormatCtx, 0, pInfmt, 0, formatParams) < 0)
  
     return -1; // Couldn't open device
  
  
  
  /* Same as video4linux code*/

  So another question is : how many devices are supported by Libav ? All I have found about capture cameras output with libav on windows is advice to use DirectShow for this purpose because libav supports too few devices. Maybe situation has already changed now and it does support enough devices to use it in production applications ?

  If this isn't possible.. Well I hope my question won't be useless and this composed from different sources piece of code will help someone interested in this theme 'coz there are really too few information about it in the whole internet.

• What are the specifications of Flex usable FLV videos ?

  26 septembre 2011, par Riduidel

  I have a server which streams FLV files to a Flex client.
  In this flex client, the video timeline advances incoherently, and no video can be seen on screen (only the sound can be heard).

  My FLV file has been generated using ffmpeg, which says (about this generated file)

  FFmpeg version 0.6, Copyright (c) 2000-2010 the FFmpeg developers
  
    built on Aug  8 2010 04:24:04 with gcc 4.3.2
  
    configuration: --prefix=/home/marpada/ffmpegfull --enable-gpl --enable-version3 --enable-nonfree --disable-ffplay --disable-ffserver --enable-libmp3lame --enable-libfaac --enable-libvpx --enable-libfaad --enable-libvorbis --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libxvid --enable-libx264 --enable-libtheora --extra-ldflags=-static --extra-libs='-lvorbis -logg -lxvidcore -lx264 -lopencore-amrnb -lopencore-amrwb -lfaad -lfaac -lvpx -ltheora -lm -lpthread' --enable-small --enable-runtime-cpudetect
  
    libavutil     50.15. 1 / 50.15. 1
  
    libavcodec    52.72. 2 / 52.72. 2
  
    libavformat   52.64. 2 / 52.64. 2
  
    libavdevice   52. 2. 0 / 52. 2. 0
  
    libswscale     0.11. 0 /  0.11. 0
  
  [flv @ 0x95c6aa0]Estimating duration from bitrate, this may be inaccurate
  
  
  
  Seems stream 0 codec frame rate differs from container frame rate: 1000.00 (1000/1) -> 25.00 (25/1)
  
  Input #0, flv, from '/appli/perigee_70ri/data/files/ged_bur%0/Imagettes/70ri/279/2/8/20_109021138o.70ri_FLV_preview_.flv':
  
    Metadata:
  
      hasMetadata     : true
  
      hasVideo        : true
  
      hasAudio        : true
  
      duration        : 589
  
      lasttimestamp   : 589
  
      lastkeyframetimestamp: 589
  
      width           : 352
  
      height          : 288
  
      videodatarate   : 199
  
      framerate       : 25
  
      audiodatarate   : 125
  
      audiosamplerate : 44100
  
      audiosamplesize : 16
  
      stereo          : true
  
      filesize        : 25058444
  
      videosize       : 15195503
  
      audiosize       : 9690850
  
      datasize        : 23027
  
      metadatacreator : flvmeta 1.1-r202
  
      audiocodecid    : 2
  
      videocodecid    : 2
  
      audiodelay      : 0
  
      canSeekToEnd    : false
  
      hasCuePoints    : false
  
      hasKeyframes    : true
  
    Duration: 00:09:48.78, start: 0.000000, bitrate: 332 kb/s
  
      Stream #0.0: Video: flv, yuv420p, 352x288, 204 kb/s, 25 tbr, 1k tbn, 1k tbc
  
      Stream #0.1: Audio: mp3, 44100 Hz, 2 channels, s16, 128 kb/s
  
  At least one output file must be specified

  Which, as far as it seems to me, is OK.

  Furthermore, the video plays nice in VLC.