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• FFmpeg/Libav audio decode example

  19 mai 2015, par Walid Baccari

  I am trying to get the same output as that of ffmpeg/avconv from converting an MP2 file to raw PCM using code. I used the audio_decode_example function from the tutorial included in the FFmpeg/Libav documentation but the outputs were different.

  What steps does the ffmpeg/avconv command perform that I need to add to my program to get the same output ?

  Edit :
  This is the output from avconv -v debug -i test.mp2 test.sw :

  avconv version v10_beta1-302-g606cc8a, Copyright (c) 2000-2014 the Libav developers
  
  built on Mar 20 2014 20:28:32 with gcc 4.8 (Ubuntu/Linaro 4.8.1-10ubuntu9)
  
  configuration: 
  
  libavutil     53.  6. 0 / 53.  6. 0
  
  libavcodec    55. 34. 1 / 55. 34. 1
  
  libavformat   55. 12. 0 / 55. 12. 0
  
  libavdevice   54.  0. 0 / 54.  0. 0
  
  libavfilter    4.  3. 0 /  4.  3. 0
  
  libavresample  1.  2. 0 /  1.  2. 0
  
  libswscale     2.  1. 2 /  2.  1. 2
  
  Splitting the commandline.
  
  Reading option '-v' ... matched as option 'v' (set libav* logging level) with argument 'debug'.
  
  Reading option '-i' ... matched as input file with argument 'test.mp2'.
  
  Reading option 'test1.sw' ... matched as output file.                                  
  
  Finished splitting the commandline.                                       
  
  Parsing a group of options: global .                
  
  Applying option v (set libav* logging level) with argument debug.
  
  Successfully parsed a group of options.
  
  Parsing a group of options: input file test.mp2.
  
  Successfully parsed a group of options.
  
  Opening an input file: test.mp2.
  
  [mp3 @ 0x27e5060] Probed with size=2048 and score=51
  
  [mp3 @ 0x27e5060] Estimating duration from bitrate, this may be inaccurate
  
  Guessed Channel Layout for  Input Stream #0.0 : stereo
  
  Input #0, mp3, from 'test.mp2':
  
    Duration: 00:00:04.80, start: 0.000000, bitrate: 64 kb/s
  
      Stream #0.0, 200, 1/14112000: Audio: mp2, 48000 Hz, stereo, s16p, 64 kb/s
  
  Successfully opened the file.
  
  Parsing a group of options: output file test1.sw.
  
  Successfully parsed a group of options.
  
  Opening an output file: test1.sw.
  
  Successfully opened the file.
  
  Detected 2 logical cores.
  
  [abuffer @ 0x27e5860] tb:1/48000 samplefmt:s16p samplerate: 48000 ch layout:0x3
  
  [abuffersink @ 0x2807040] auto-inserting filter 'auto-inserted fifo 0' between the filter 'audio format for output stream 0:0' and the filter 'output stream 0:0'
  
  [aformat @ 0x2806bc0] auto-inserting filter 'auto-inserted resampler 0' between the filter 'Parsed filter 0 anull' and the filter 'audio format for output stream 0:0'
  
  [AVAudioResampleContext @ 0x28092a0] audio_convert: found function: s16p to s16  (C)
  
  [AVAudioResampleContext @ 0x28092a0] audio_convert: found function: s16p to s16  (SSE2)
  
  [resample @ 0x2808560] fmt:s16p srate:48000 cl:stereo -> fmt:s16 srate:48000 cl:stereo
  
  Output #0, s16le, to 'test1.sw':
  
    Metadata:
  
      encoder         : Lavf55.12.0
  
      Stream #0.0, 0, 1/90000: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
  
    Stream mapping:
  
      Stream #0:0 -> #0:0 (mp2 -> pcm_s16le)
  
  Press ctrl-c to stop encoding
  
  Input stream #0:0 frame changed from rate:48000 fmt:s16p ch:2 chl:stereo to rate:48000 fmt:s16 ch:2 chl:stereo
  
  Detected 2 logical cores.
  
  [abuffer @ 0x2806e40] tb:1/48000 samplefmt:s16 samplerate: 48000 ch layout:0x3
  
  [abuffersink @ 0x2806fa0] auto-inserting filter 'auto-inserted fifo 0' between the filter 'audio format for output stream 0:0' and the filter 'output stream 0:0'
  
  No more output streams to write to, finishing.
  
  size=     900kB time=4.80 bitrate=1536.0kbits/s    
  
  video:0kB audio:0kB global headers:0kB muxing overhead 0.000000%

• Splitting webm video to png with transparency

  24 août 2016, par Stephen Emslie

  I need to split a webm encoded video into png frames, without losing transparency. I use the following ffmpeg command :

  ffmpeg -i dancer1.webm -pix_fmt rgba frames/%04d.png

  This produces a directory of pngs, but why is each output frame is missing transparency ?

  I have used this example video, which contains an alpha channel. See it playing over a background here. Here’s an example output frame from ffmpeg :

  

  ffmpeg produces the following output when it runs :

  ffmpeg version N-60294-g549f052 Copyright (c) 2000-2014 the FFmpeg developers                                             [1/2471]
  
    built on Feb  2 2014 05:41:56 with gcc 4.6 (Debian 4.6.3-1)
  
    configuration: --prefix=/root/ffmpeg-static/64bit --extra-cflags='-I/root/ffmpeg-static/64bit/include -static' --extra-ldflags='-L/root/ffmpeg-static/64bit/lib -static' --extra-libs='-lxml2 -lexpat -lfreetype' --enable-static --disable-shared --disable-ffserver --disable-doc --enable-bzlib --enable-zlib --enable-postproc --enable-runtime-cpudetect --enable-libx264 --enable-gpl --enable-libtheora --enable-libvorbis --enable-libmp3lame --enable-gray --enable-libass --enable-libfreetype --enable-libopenjpeg --enable-libspeex --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-version3 --enable-libvpx
  
    libavutil      52. 63.100 / 52. 63.100
  
    libavcodec     55. 49.101 / 55. 49.101
  
    libavformat    55. 28.101 / 55. 28.101
  
    libavdevice    55.  7.100 / 55.  7.100
  
    libavfilter     4.  1.101 /  4.  1.101
  
    libswscale      2.  5.101 /  2.  5.101
  
    libswresample   0. 17.104 /  0. 17.104
  
    libpostproc    52.  3.100 / 52.  3.100
  
  Input #0, matroska,webm, from 'dancer1.webm':
  
    Metadata:
  
      encoder         : libwebm-0.2.1.0
  
    Duration: 00:01:02.83, start: 0.000000, bitrate: 520 kb/s
  
      Stream #0:0(eng): Video: vp8, yuv420p, 640x360, SAR 1:1 DAR 16:9, 30 tbr, 1k tbn, 1k tbc (default)
  
      Metadata:
  
        alpha_mode      : 1
  
  Output #0, image2, to 'frames/%04d.png':
  
    Metadata:
  
      encoder         : Lavf55.28.101
  
      Stream #0:0(eng): Video: png, rgba, 640x360 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 90k tbn, 30 tbc (default)
  
  Metadata:
  
    alpha_mode      : 1
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (vp8 -> png)

  Running identify on an output png produces this :

  $ identify 0001.png
  
  0001.png PNG 640x360 640x360+0+0 8-bit DirectClass 94.1KB 0.000u 0:00.000

  file has this to say about the png :

  $ file 0001.png
  
  0001.png: PNG image data, 640 x 360, 8-bit/color RGBA, non-interlaced

  Everything looks about right to me, so why don’t the output images contain an alpha channel ?

• Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height

  20 mars 2014, par user3441169

  I need to convert a video file from .flv to .mp4.

  When ever run the my application getting the exception.

  Please find the below my ffmpeg command along with error.

  Command :

  /usr/bin/avconv -y -i /home/veera/Desktop/videos/Prasad.Daily-2014-03-19.flv -vcodec libx264 -r 30000/1001 -b:v 250k -bt 250k -s 1280x720 -acodec libvo_aacenc -ar 32000 -ab 48k -crf 22 -profile:v baseline -level 1 -movflags +faststart -preset veryfast /home/veera/Desktop/videos/resized.mp4

  Output :

  ERROR>Stream mapping :

  ERROR> Stream #0:0 -> #0:0 (h264 -> libx264)

  ERROR> Stream #0:1 -> #0:1 (aac -> libvo_aacenc)

  ERROR>Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height

  ExitValue : 1