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• How can I programmatically delete frames from an mpg video and keep the audio in sync ?

  22 janvier 2018, par Pima omg

  I stream training videos from work, but don’t have a great connection and get a lot of buffering. I have captured the streamed video from the PC screen into an mpg file. Fortunately when the video buffers, it shows a characteristic buffering icon in the center of the screen and there is no sound. Using ffmpeg, I have been able to write a c++ method that can step through the video frames of the mpeg file, convert to an RBG frame and detect the presence or absence of this characteristic buffering icon.

  The final thing I need to do is generate a new mpeg file with only the frames that do not have this buffering image, and keep all the audio in sync. How do I do that with ffmpeg ?

  I have already found the dts and pts timestamps on the video and audio frames, but don’t know how to use this information to recode just the frames that don’t have the buffering image. The recode should keep all the properties of the original (framerate, resolution, size etc)

  Here is the stripped down code I use to traverse the frame and detect which ones I want to keep (omitting a lot of initialization and error checking)

  while (av_read_frame(pFormatCtx, &packet) >= 0)
  
      {
  
          // Is this a packet from the video stream?
  
          if (packet.stream_index == videoStream)
  
          {
  
              // Decode video frame
  
              avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
  
  
  
              // Did we get a video frame?
  
              if (frameFinished)
  
              {
  
                  // Convert the image from its native format to RGB
  
                  sws_scale(sws_ctx, (uint8_t const * const *)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameRGB->data, pFrameRGB->linesize);
  
                  if (ThisIsAFrameIWant(pFrameRGB))
  
                  {
  
                      WRITE FRAME TO NEW MPEG KEEPING AUDIO IN SYNC
  
                  }
  
              }
  
          }
  
      }

• ffmpeg muxing ismv&isma to mp4 resulting in wrong frame rates

  4 janvier 2018, par Frank Toxic

  I have problems muxing fragmented video and audio tracks (piff) to an unfragmented standard mp4 including audio&video

  From a metadata mediainfo point of view everything looks ok, Codec ID is mp41 not mp42 but shouldn’t be a big problem

  General
  
  Complete name                            : D:\Temp\output.mp4
  
  Format                                   : MPEG-4
  
  Format profile                           : Base Media
  
  Codec ID                                 : isom (isom/iso2/avc1/mp41)
  
  File size                                : 2.76 GiB
  
  Duration                                 : 43 min 11 s
  
  Overall bit rate mode                    : Constant
  
  Overall bit rate                         : 9 161 kb/s
  
  Writing application                      : Lavf57.83.100
  
  
  
  Video
  
  ID                                       : 1
  
  Format                                   : AVC
  
  Format/Info                              : Advanced Video Codec
  
  Format profile                           : Main@L4
  
  Format settings, CABAC                   : Yes
  
  Format settings, ReFrames                : 4 frames
  
  Codec ID                                 : avc1
  
  Codec ID/Info                            : Advanced Video Coding
  
  Duration                                 : 43 min 11 s
  
  Source duration                          : 14 s 460 ms
  
  Bit rate mode                            : Constant
  
  Bit rate                                 : 9 000 kb/s / 9 000 kb/s
  
  Width                                    : 1 920 pixels
  
  Height                                   : 1 080 pixels
  
  Display aspect ratio                     : 16:9
  
  Frame rate mode                          : Constant
  
  Frame rate                               : 25.000 FPS
  
  Color space                              : YUV
  
  Chroma subsampling                       : 4:2:0
  
  Bit depth                                : 8 bits
  
  Scan type                                : Progressive
  
  Bits/(Pixel*Frame)                       : 0.174
  
  Stream size                              : 2.71 GiB (98%)
  
  Source stream size                       : 2.71 GiB (98%)
  
  Writing library                          : x264 core 152
  
  Encoding settings                        : cabac=1 / ref=2 / deblock=1:-1:-1 / analyse=0x1:0x131 / me=umh / subme=10 / psy=1 / psy_rd=1.00:0.15 / mixed_ref=1 / me_range=24 / chroma_me=1 / trellis=2 / 8x8dct=0 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-3 / threads=36 / lookahead_threads=3 / sliced_threads=0 / slices=1 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / stitchable=1 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=50 / keyint_min=2 / scenecut=0 / intra_refresh=0 / rc_lookahead=50 / rc=cbr / mbtree=1 / bitrate=9000 / ratetol=1.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / vbv_maxrate=9000 / vbv_bufsize=9000 / nal_hrd=cbr / filler=1 / ip_ratio=1.40 / aq=3:1.00
  
  Language                                 : English
  
  mdhd_Duration                            : 2591440
  
  
  
  Audio
  
  ID                                       : 2
  
  Format                                   : AAC
  
  Format/Info                              : Advanced Audio Codec
  
  Format profile                           : LC
  
  Codec ID                                 : 40
  
  Duration                                 : 43 min 11 s
  
  Bit rate mode                            : Constant
  
  Bit rate                                 : 157 kb/s
  
  Channel(s)                               : 2 channels
  
  Channel positions                        : Front: L R
  
  Sampling rate                            : 48.0 kHz
  
  Frame rate                               : 46.875 FPS (1024 spf)
  
  Compression mode                         : Lossy
  
  Stream size                              : 48.4 MiB (2%)
  
  Language                                 : German
  
  Default                                  : Yes
  
  Alternate group                          : 1

  The actual problem is the frame rate missmatch, reported by Baton or visible in Windows Explorer -> Properties -> Details

  Mismatch in system and elementary metadata.  System Level  
  
    
  
  For video track ID 1, Frame Rate at the system level is 4482.79 fps, whereas at the elementary level it is 25.00 fps. Specified criteria: Report as Serious if  Mismatch in Frame Rate detected

  Windows Explorer Details

  ffmpeg cmd line used

  D:\FFMPEG\bin>ffmpeg.exe -i "D:\Temp\video.ismv" -i "D:\Temp\audio.isma" -codec copy "D:\Temp\output.mp4"
  
  ffmpeg version 3.4.1 Copyright (c) 2000-2017 the FFmpeg developers
  
    built with gcc 7.2.0 (GCC)
  
    configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-bzlib --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable
  
  -libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --e
  
  nable-libvidstab --enable-libvorbis --enable-cuda --enable-cuvid --enable-d3d11va --enable-nvenc --enable-dxva2 --enable-avisynth --enable-libmfx
  
    libavutil      55. 78.100 / 55. 78.100
  
    libavcodec     57.107.100 / 57.107.100
  
    libavformat    57. 83.100 / 57. 83.100
  
    libavdevice    57. 10.100 / 57. 10.100
  
    libavfilter     6.107.100 /  6.107.100
  
    libswscale      4.  8.100 /  4.  8.100
  
    libswresample   2.  9.100 /  2.  9.100
  
    libpostproc    54.  7.100 / 54.  7.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'D:\Temp\video.ismv':
  
    Metadata:
  
      major_brand     : piff
  
      minor_version   : 1
  
      compatible_brands: iso2piff
  
    Duration: 00:43:11.44, start: 0.080000, bitrate: 9000 kb/s
  
      Stream #0:0(eng): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 8998 kb/s, 25 fps, 25 tbr, 10000k tbn, 50 tbc (default)
  
      Metadata:
  
        handler_name    : USP Video Handler
  
        encoder         : AVC Coding
  
  Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 'D:\Temp\audio.isma':
  
    Metadata:
  
      major_brand     : piff
  
      minor_version   : 1
  
      compatible_brands: iso2piff
  
    Duration: 00:43:11.40, start: 0.000000, bitrate: 160 kb/s
  
      Stream #1:0(deu): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 156 kb/s (default)
  
      Metadata:
  
        handler_name    : USP Sound Handler
  
  Output #0, mp4, to 'D:\Temp\output.mp4':
  
    Metadata:
  
      major_brand     : piff
  
      minor_version   : 1
  
      compatible_brands: iso2piff
  
      encoder         : Lavf57.83.100
  
      Stream #0:0(eng): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 8998 kb/s, 25 fps, 25 tbr, 10000k tbn, 10000k tbc (default)
  
      Metadata:
  
        handler_name    : USP Video Handler
  
        encoder         : AVC Coding
  
      Stream #0:1(deu): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 156 kb/s (default)
  
      Metadata:
  
        handler_name    : USP Sound Handler
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (copy)
  
    Stream #1:0 -> #0:1 (copy)
  
  Press [q] to stop, [?] for help
  
  frame=64786 fps=4397 q=-1.0 Lsize= 2898087kB time=00:43:11.38 bitrate=9161.6kbits/s speed= 176x
  
  video:2846633kB audio:49555kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.065580%

• How to use scale filter in doc/examples/transcoding.c

  19 janvier 2018, par siods333333

  I tried to replace the "null" filter with the "scale=320x180" filter in the doc/examples/transcoding.c file, it only resulted into the this error message :

  [libx264 @ 03303ee0] Input picture width (640) is greater than stride (256)
  
  Error occurred: Generic error in an external library

  What is wrong ? Look that init_filters happens after open_output_file, the encoder is already set before it even knows the resolution of the output.

  How to do this properly ?

  Look at this piece of code, I don’t get what it’s talking about, fiters ain’t going to magically set the correct resolution :

          /* In this example, we transcode to same properties (picture size,
  
           * sample rate etc.). These properties can be changed for output
  
           * streams easily using filters */
  
          if (dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO) {
  
              enc_ctx->height = dec_ctx->height;
  
              enc_ctx->width = dec_ctx->width;

  Found this in the ffmpeg.c itself :

      enc_ctx->width  = av_buffersink_get_w(ost->filter->filter);
  
      enc_ctx->height = av_buffersink_get_h(ost->filter->filter);