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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 ?

• Split video with ffmpeg segment option is missing frame

  9 février 2024, par Dan

  I’m trying to get the ffmpeg “segment” option to split my video into segments at the Iframes. I'm using ffmpeg V6.1.1.

  


  First I added time stamps to each frame of my video so that when it plays, I can see exactly which frame is being displayed. I used this command :

  


  ffmpeg -i In.mp4 -vf "drawtext=fontfile='C :\Windows\Fonts\Arial.ttf' : text='%frame_num :~ %pts':fontsize=200 : r=25 : x=(w-tw)/2 : y=h-(2*lh) : fontcolor=white : box=1 : boxcolor=0x00000099" -y Out.mp4

  


  Then I used ffprobe to confirm that the video is 30 FPS and the Iframes are as follows :

  


  0.000000
4.933333
10.000000
11.533333
18.866667
24.966667

  


  Based on these Iframe times, I’d expect the following segments :

  


  





  


  


  


  


  


  


  



  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  Start Frame	Start Time	End Frame	End Time
  0	0	147	4.900000
  148	4.933333	299	9.966667
  300	10.000000	345	11.500000
  346	11.533333	565	18.833334
  566	18.866667	748	24.933334
  749	24.966667	867	28.906667

  


  


  When I use ffmpeg to split the video into segments with the following command, I get six files as expected :

  


  ffmpeg -i Out.mp4 -f segment -c copy -reset_timestamps 1 -map 0 "Out %d.mp4"

  


  When I play the segments, they are all correct except the first segment file (Out 0.mp4). It seems to be missing the last frame. It contains frames 0 to 146 (4.866667 sec) but should also include frame 147 (4.9 sec). All the other segment files are as expected.

  


  I’ve tried this on several different mp4 videos and they all are missing the last frame on the first segments.

  


  Any idea why my first segment files is missing the last frame of the segment ?

  


  Could this be an ffmpeg bug ?

  


  Thanks for the help !
Dan

  


  Here is my console session with all output :

  


  C:\> ffprobe Out.mp4
ffprobe version 2023-12-21-git-1e42a48e37-full_build-www.gyan.dev Copyright (c) 2007-2023 the FFmpeg developers
  built with gcc 12.2.0 (Rev10, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --pkg-config=pkgconf --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-libsnappy --enable-zlib --enable-librist --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-libbluray --enable-libcaca --enable-sdl2 --enable-libaribb24 --enable-libaribcaption --enable-libdav1d --enable-libdavs2 --enable-libuavs3d --enable-libzvbi --enable-librav1e --enable-libsvtav1 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs2 --enable-libxvid --enable-libaom --enable-libjxl --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-liblensfun --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc --enable-dxva2 --enable-d3d11va --enable-libvpl --enable-libshaderc --enable-vulkan --enable-libplacebo --enable-opencl --enable-libcdio --enable-libgme --enable-libmodplug --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libshine --enable-libtheora --enable-libtwolame --enable-libvo-amrwbenc --enable-libcodec2 --enable-libilbc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-ladspa --enable-libbs2b --enable-libflite --enable-libmysofa --enable-librubberband --enable-libsoxr --enable-chromaprint
  libavutil      58. 36.100 / 58. 36.100
  libavcodec     60. 36.100 / 60. 36.100
  libavformat    60. 20.100 / 60. 20.100
  libavdevice    60.  4.100 / 60.  4.100
  libavfilter     9. 14.100 /  9. 14.100
  libswscale      7.  6.100 /  7.  6.100
  libswresample   4. 13.100 /  4. 13.100
  libpostproc    57.  4.100 / 57.  4.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Out.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    title           : Short 4k video sample - 4K Ultra HD (3840x2160)
    date            : 2014:05:24 19:00:00
    encoder         : Lavf60.20.100
  Duration: 00:00:28.96, start: 0.000000, bitrate: 3181 kb/s
  Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 1920x1080 [SAR 1:1 DAR 16:9], 3045 kb/s, 30 fps, 30 tbr, 15360 tbn (default)
      Metadata:
        handler_name    : VideoHandler
        vendor_id       : [0][0][0][0]
        encoder         : Lavc60.36.100 libx264
  Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
      Metadata:
        handler_name    : SoundHandler
        vendor_id       : [0][0][0][0]

C:\ ffprobe -loglevel error -skip_frame nokey -select_streams v:0 -show_entries frame=pts_time -of csv=print_section=0 Out.mp4
0.000000,
4.933333
10.000000
11.533333
18.866667
24.966667

C:\ ffmpeg -i Out.mp4 -f segment -c copy -reset_timestamps 1 -map 0 "Out %1d.mp4"
ffmpeg version 2023-12-21-git-1e42a48e37-full_build-www.gyan.dev Copyright (c) 2000-2023 the FFmpeg developers
  built with gcc 12.2.0 (Rev10, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --pkg-config=pkgconf --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-libsnappy --enable-zlib --enable-librist --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-libbluray --enable-libcaca --enable-sdl2 --enable-libaribb24 --enable-libaribcaption --enable-libdav1d --enable-libdavs2 --enable-libuavs3d --enable-libzvbi --enable-librav1e --enable-libsvtav1 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs2 --enable-libxvid --enable-libaom --enable-libjxl --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-liblensfun --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc --enable-dxva2 --enable-d3d11va --enable-libvpl --enable-libshaderc --enable-vulkan --enable-libplacebo --enable-opencl --enable-libcdio --enable-libgme --enable-libmodplug --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libshine --enable-libtheora --enable-libtwolame --enable-libvo-amrwbenc --enable-libcodec2 --enable-libilbc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-ladspa --enable-libbs2b --enable-libflite --enable-libmysofa --enable-librubberband --enable-libsoxr --enable-chromaprint
  libavutil      58. 36.100 / 58. 36.100
  libavcodec     60. 36.100 / 60. 36.100
  libavformat    60. 20.100 / 60. 20.100
  libavdevice    60.  4.100 / 60.  4.100
  libavfilter     9. 14.100 /  9. 14.100
  libswscale      7.  6.100 /  7.  6.100
  libswresample   4. 13.100 /  4. 13.100
  libpostproc    57.  4.100 / 57.  4.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Out.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    title           : Short 4k video sample - 4K Ultra HD (3840x2160)
    date            : 2014:05:24 19:00:00
    encoder         : Lavf60.20.100
  Duration: 00:00:28.96, start: 0.000000, bitrate: 3181 kb/s
  Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 1920x1080 [SAR 1:1 DAR 16:9], 3045 kb/s, 30 fps, 30 tbr, 15360 tbn (default)
      Metadata:
        handler_name    : VideoHandler
        vendor_id       : [0][0][0][0]
        encoder         : Lavc60.36.100 libx264
  Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
      Metadata:
        handler_name    : SoundHandler
        vendor_id       : [0][0][0][0]
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
[segment @ 00000195bbc52940] Opening 'Out 0.mp4' for writing
Output #0, segment, to 'Out %1d.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    title           : Short 4k video sample - 4K Ultra HD (3840x2160)
    date            : 2014:05:24 19:00:00
    encoder         : Lavf60.20.100
  Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 3045 kb/s, 30 fps, 30 tbr, 15360 tbn (default)
      Metadata:
        handler_name    : VideoHandler
        vendor_id       : [0][0][0][0]
        encoder         : Lavc60.36.100 libx264
  Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
      Metadata:
        handler_name    : SoundHandler
        vendor_id       : [0][0][0][0]
Press [q] to stop, [?] for help
[segment @ 00000195bbc52940] Opening 'Out 1.mp4' for writing
[segment @ 00000195bbc52940] Opening 'Out 2.mp4' for writing
[segment @ 00000195bbc52940] Opening 'Out 3.mp4' for writing
[segment @ 00000195bbc52940] Opening 'Out 4.mp4' for writing
[segment @ 00000195bbc52940] Opening 'Out 5.mp4' for writing
[out#0/segment @ 00000195bc3e8cc0] video:10757kB audio:456kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
size=N/A time=00:00:28.86 bitrate=N/A speed= 322x