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• FFmpeg library : modified muxing sample for FLTP input and FLTP audio, loses audio

  21 janvier 2014, par taansari

  Based on muxing sample that comes with FFmpeg docs, I have modified it, from input format as S16 to FLTP (planar stereo), and outputting to webm format (stereo).

  Since input is now FLTP, I am filling two arrays, then encoding again to FLTP. There are no obvious errors given on screen, but the resulting webm video does not play any audio (just the video content). This is just proof of concept in understanding things ; here is an added (crude) function to fill up input FLTP stereo buffer :

  static void get_audio_frame_for_planar_stereo(int16_t **samples, int frame_size, int nb_channels)
  
  {
  
      int j, i, v[2];
  
      int16_t *q1 = (int16_t *) samples[0];
  
      int16_t *q2 = (int16_t *) samples[1];
  
  
  
      for (j = 0; j < frame_size; j++)
  
      {
  
          v[0] = (int)(sin(t) * 10000);
  
          v[1] = (int)(tan(t) * 10000);
  
          *q1++ = v[0];
  
          *q2++ = v[1];
  
          t     += tincr;
  
          tincr += tincr2;
  
      }
  
  }

  Which I am calling from inside write_audio_frame() function.

  Note also, wherever code reffered AV_SAMPLE_FMT_S16 as input, I have changed to AV_SAMPLE_FMT_FLTP.

  Whole workable source is here :

  https://gist.github.com/anonymous/05d1d7662e9feafc45a6

  When run with ffprobe.exe, with these instructions :

  ffprobe -show_packets output.webm >output.txt

  I see nothing out of ordinary, all pts/dts values appear to be in place :

  https://gist.github.com/anonymous/3ed0d6308700ab991704

  Could someone highlight cause of this mis-interpretation ?

  Thanks for your time...

  p.s. I am using Zeranoe FFmpeg Windows builds (32 bit), built on Jan 9 2014 22:04:35 with gcc 4.8.2.(GCC)

  Edit : Based on your guidance elsewhere, I tried the following :

      /* set options */
  
      //av_opt_set_int       (swr_ctx, "in_channel_count",   c->channels,       0);
  
      //av_opt_set_int       (swr_ctx, "in_sample_rate",     c->sample_rate,    0);
  
      //av_opt_set_sample_fmt(swr_ctx, "in_sample_fmt",      AV_SAMPLE_FMT_FLTP, 0);
  
      //av_opt_set_int       (swr_ctx, "out_channel_count",  c->channels,       0);
  
      //av_opt_set_int       (swr_ctx, "out_sample_rate",    c->sample_rate,    0);
  
      //av_opt_set_sample_fmt(swr_ctx, "out_sample_fmt",     c->sample_fmt,     0);
  
  
  
      av_opt_set_int(swr_ctx, "in_channel_layout",    AV_CH_LAYOUT_STEREO, 0);
  
      av_opt_set_int(swr_ctx, "in_sample_rate",       c->sample_rate, 0);
  
      av_opt_set_sample_fmt(swr_ctx, "in_sample_fmt", AV_SAMPLE_FMT_FLTP, 0);
  
  
  
      av_opt_set_int(swr_ctx, "out_channel_layout",    AV_CH_LAYOUT_STEREO, 0);
  
      av_opt_set_int(swr_ctx, "out_sample_rate",       c->sample_rate, 0);
  
      av_opt_set_sample_fmt(swr_ctx, "out_sample_fmt", AV_SAMPLE_FMT_FLTP, 0);

  And the revised function :

  static void get_audio_frame_for_planar_stereo(uint8_t **samples, int frame_size, int nb_channels)
  
  {
  
      int j, i;
  
      float v[2];
  
      float *q1 = (float *) samples[0];
  
      float *q2 = (float *) samples[1];
  
  
  
      for (j = 0; j < frame_size; j++) 
  
      {
  
          v[0] = (tan(t) * 1);
  
          v[1] = (sin(t) * 1);
  
          *q1++ = v[0];
  
          *q2++ = v[1];
  
          t     += tincr;
  
          tincr += tincr2;
  
      }
  
  }

  Now it appears to be working properly. I tried changing function parameters from uint8_t** to float**, as well as src_samples_data from uint8_t** to float**, but did not make any difference, in a view.

  Updated code : https://gist.github.com/anonymous/35371b2c106961029c3d

  Thanks for highlighting the place(s) that result in this behavior !

• lavr : Do not change the sample format for mono audio

  18 juillet 2014, par Justin Ruggles

  lavr : Do not change the sample format for mono audio
  This treats mono as planar internally within libavresample rather
  
  than changing the sample format.
  Signed-off-by : Luca Barbato <lu_zero@gentoo.org>
  

  • [DBH] libavresample/audio_convert.c
  • [DBH] libavresample/audio_data.c
  • [DBH] libavresample/audio_data.h
  • [DBH] libavresample/utils.c

• ffmpeg : Cover image for video

  15 avril 2014, par Michael Herrmann

  I have a video file video.mp4 with sound (file information and download links below). I also have an image cover.png which contains a logo and a caption for the video. I want to create a new video which starts by showing cover.png, then blends in the first frame of video.mp4 within one second, then continues to play video.mp4.

  My failed attempt :

  I used ffmpeg to extract the first frame of video.mp4 into image file first_frame.png. I then created video fade.mp4 with a transition from cover.png to first_frame.png :

  ffmpeg -loop 1 -i cover.png -r 24 -loop 1 -i first_frame.png -r 24 -filter_complex "[1:v][0:v]blend=all_expr='A*(if(gte(T,1),1,T/1))+B*(1-(if(gte(T,1),1,T/1)))'" -t 2 fade.mp4

  I then wanted to simply concatenate fade.mp4 and video.mp4 to produce the desired result. I created a file mylist.txt with the following contents :

  file 'fade.mp4'
  
  file 'video.mp4'

  Then I issued the following command to ffmpeg :

  ffmpeg -f concat -i mylist.txt -c copy out.mp4

  Unfortunately, this produced a lot of warnings of the following form :

  [concat @ 00000000003580e0] Invalid stream index 1:01:24.05 bitrate= 136.3kbits/s

  The resulting video out.mp4 does correctly start with fade.mp4, but unfortunately continues with completely random colour patterns when it comes to playing video.mp4.

  File information for video.mp4 :

  • Stream 0 :
    • Type : Video
    • Codec : H264 - MPEG-4 AVC (part10) (avc1)
    • Resolution : 800x600
    • Frame rate : 24
    • Decoded format : Planar 4:2:0 YUV
  • Stream 1 :
    • Type : Audio
    • Codec : MPEG Audio layer 1/2/3 (mpga)
    • Channels : Mono
    • Sample rate : 16000 Hz
    • Bitrate : 24 kb/s

  File information for cover.png :

  • Resolution : 800x600

  Links to files :

  • video.mp4 : https://www.dropbox.com/s/ci5wlz7abn232go/video.mp4
  • cover.png : https://www.dropbox.com/s/8eeon1j213s6l5x/cover.png
  • first_frame.mp4 : https://www.dropbox.com/s/hrxzcdjki0b9xqt/first_frame.png
  • fade.mp4 : https://www.dropbox.com/s/ohuf98xn3gmkniq/fade.mp4
  • mylist.txt : https://www.dropbox.com/s/kjqnzsa50uslqcr/mylist.txt
  • out.mp4 : https://www.dropbox.com/s/0h27z7ahjg3pbbw/out.mp4