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• MPEG-2 AAC frame-by-frame audio decoding

  3 mai 2018, par Jonathan May

  I have individual audio frames encoded in MPEG-2 AAC. Each frame consists of 1024 16 bit PCM samples.

  I notice that each AAC frame is a different size. I assume this is a result of the MPEG-2 AAC compression algorithm and perfectly normal.

  I need a way to decode a single frame and get back the original 1024 PCM samples (with error from lossy compression, that’s fine).

  I couldn’t find information about the MPEG-2 AAC algorithm ANYWHERE online. It’s kinda nuts.

  I’ve been trying a crude work around using a library called pydub, which contains a few methods which use FFMPEG’s AAC decoder. Trying to load the audio frame as an AudioSegment using AAC encoding :

  audioData = BytesIO(frame)
  
  sound = AudioSegment.from_file(audioData, format="aac")

  gives the following error :

  [aac @ 000002d444c1aa00] Estimating duration from bitrate, this may be inaccurate\r\n
  
  Input #0, aac, from 'C:\\Users\\jmk_m\\AppData\\Local\\Temp\\tmpjl3x0xao':\r\n
  
    Duration: 00:00:00.19, bitrate: 23 kb/s\r\n
  
  Stream #0:0: Audio: aac (LC), 22050 Hz, mono, fltp, 23 kb/s\r\nStream mapping:\r\n
  
  Stream #0:0 -> #0:0 (aac (native) -> pcm_s16le (native))\r\n
  
  Press [q] to stop, [?] for help\r\n
  
  Output #0, wav, to 'C:\\Users\\jmk_m\\AppData\\Local\\Temp\\tmpxmp942e4':\r\n
  
  Metadata:\r\n
  
  ISFT            : Lavf58.10.100\r\n
  
  Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 22050 Hz, mono, s16, 352 kb/s\r\n
  
  Metadata:\r\n      encoder         : Lavc58.13.100 pcm_s16le\r\n
  
  [aac @ 000002d444cc7480] Reserved bit set.\r\n
  
  [aac @ 000002d444cc7480] Prediction is not allowed in AAC-LC.\r\n
  
  Error while decoding stream #0:0: Invalid data found when processing input\r\n
  
  [aac @ 000002d444cc7480] Reserved bit set.\r\n
  
  [aac @ 000002d444cc7480] Prediction is not allowed in AAC-LC.\r\n
  
  Error while decoding stream #0:0: Invalid data found when processing input\r\n
  
  [aac @ 000002d444cc7480] Prediction is not allowed in AAC-LC.\r\n
  
  Error while decoding stream #0:0: Invalid data found when processing input\r\n
  
  size=       2kB time=00:00:00.04 bitrate= 366.2kbits/s speed=5.45x    \r\n
  
  video:0kB audio:2kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 3.808594%\r\n
  
  Conversion failed!\r\n"

  If anyone has any insights as to what may be causing the error, or any alternative approaches, that’d be greatly appreciated !

• Reading JPEG in ffmpeg

  23 octobre 2012, par Paul Lammertsma

  I'm trying to get ffmpeg to encode several individual JPEG images into a video on Android. I've successfully built it for Android (see the configuration string at the end of this post).

  I can encode an h.263+ video with randomly generated frame content, and ffmpeg otherwise appears to work well.

  A similar question suggests that the following code should be sufficient to load an image into an AvFrame :

  // Make sure we have the codecs
  
  av_register_all();
  
  
  
  AVFormatContext *pFormatCtx;
  
  int ret = av_open_input_file(&pFormatCtx, imageFileName, NULL, 0, NULL);
  
  
  
  if (ret != 0) {
  
      printf("Can't open image file '%s': code %d, %s",
  
          imageFileName, ret, strerror(AVERROR(ret)));
  
  }

  The above returns the correct absolute file path and error :

  Failed '/sdcard/DCIM/Camera/IMG083.jpg' : code -1094995529, Unknown error : 1094995529

  Incidentally, if I omit av_register_all(), it returns with error 2.

  I've compiled ffmpeg with the following arguments :

  ./configure —target-os=linux
  —prefix=$PREFIX
  —enable-cross-compile
  —extra-libs="-lgcc"
  —arch=arm
  —cc=$PREBUILT/bin/arm-linux-androideabi-gcc
  —cross-prefix=$PREBUILT/bin/arm-linux-androideabi-
  —nm=$PREBUILT/bin/arm-linux-androideabi-nm
  —sysroot=$PLATFORM
  —extra-cflags=" -O3 -fpic -DANDROID -DHAVE_SYS_UIO_H=1 -Dipv6mr_interface=ipv6mr_ifindex -fasm -Wno-psabi -fno-short-enums -fno-strict-aliasing -finline-limit=300 $OPTIMIZE_CFLAGS "
  —enable-shared
  —enable-static
  —extra-ldflags="-Wl,-rpath-link=$PLATFORM/usr/lib -L$PLATFORM/usr/lib -nostdlib -lc -lm -ldl -llog"
  —disable-everything
  —enable-demuxer=mov
  —enable-demuxer=h264
  —disable-ffplay
  —enable-protocol=file
  —enable-avformat
  —enable-avcodec
  —enable-decoder=mjpeg
  —enable-decoder=png
  —enable-parser=h264
  —enable-encoder=h263
  —enable-encoder=h263p
  —disable-network
  —enable-zlib
  —disable-avfilter
  —disable-avdevice

  Any suggestions would be most welcome !

• Reading JPEG in ffmpeg

  16 juillet 2021, par Paul Lammertsma

  I'm trying to get ffmpeg to encode several individual JPEG images into a video on Android. I've successfully built it for Android (see the configuration string at the end of this post).

  



  I can encode an h.263+ video with randomly generated frame content, and ffmpeg otherwise appears to work well.

  



  A similar question suggests that the following code should be sufficient to load an image into an AvFrame :

  



  // Make sure we have the codecs
av_register_all();

AVFormatContext *pFormatCtx;
int ret = av_open_input_file(&pFormatCtx, imageFileName, NULL, 0, NULL);

if (ret != 0) {
    printf("Can't open image file '%s': code %d, %s",
        imageFileName, ret, strerror(AVERROR(ret)));
}


  



  The above returns the correct absolute file path and error :

  



  


  Failed '/sdcard/DCIM/Camera/IMG083.jpg' : code -1094995529, Unknown error : 1094995529

  


  



  Incidentally, if I omit av_register_all(), it returns with error 2.

  



  I've compiled ffmpeg with the following arguments :

  



  


  


  ./configure —target-os=linux 
 —prefix=$PREFIX 
 —enable-cross-compile 
 —extra-libs="-lgcc" 
 —arch=arm 
 —cc=$PREBUILT/bin/arm-linux-androideabi-gcc 
 —cross-prefix=$PREBUILT/bin/arm-linux-androideabi- 
 —nm=$PREBUILT/bin/arm-linux-androideabi-nm 
 —sysroot=$PLATFORM 
 —extra-cflags=" -O3 -fpic -DANDROID -DHAVE_SYS_UIO_H=1 -Dipv6mr_interface=ipv6mr_ifindex -fasm -Wno-psabi -fno-short-enums -fno-strict-aliasing -finline-limit=300 $OPTIMIZE_CFLAGS " 
 —enable-shared 
 —enable-static 
 —extra-ldflags="-Wl,-rpath-link=$PLATFORM/usr/lib -L$PLATFORM/usr/lib -nostdlib -lc -lm -ldl -llog" 
 —disable-everything 
 —enable-demuxer=mov 
 —enable-demuxer=h264 
 —disable-ffplay 
 —enable-protocol=file 
 —enable-avformat 
 —enable-avcodec 
 —enable-decoder=mjpeg 
 —enable-decoder=png 
 —enable-parser=h264 
 —enable-encoder=h263 
 —enable-encoder=h263p 
 —disable-network 
 —enable-zlib 
 —disable-avfilter 
 —disable-avdevice

  


  


  



  Any suggestions would be most welcome !