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• FFmpeg on iPhone - Modifying Video Orientation

  6 avril 2015, par Matthew McGoogan

  I’m messing with h264 videos loaded with FFmpeg on the iPhone 3GS. The problem is any videos recorded in "Portrait" orientation have a transformation matrix applied to them causing them to display rotated 90 degrees counter-clock.

  From what I understand thus far, I just need to modify the transform matrix in the ’tkhd’ atom. The problem is I am having trouble accessing or modifying this data. I checked out the FFmpeg implementation for :

  static int mov_read_tkhd(MOVContext *c, ByteIOContext *pb, MOVAtom atom)

  which clearly shows how the matrix is accessed in avformat but when I try to access the header bytes using the same functions I am not getting any rational values. Even if I were to successfully pull the matrix I’m not sure how to replace it ? FFmpeg has functions for retrieving and appending to the track header but nothing for replace it seems ?

  Any help would be greatly appreciated.

  Thanks,
  Matt.

• Which value exactly tells the video stream bit rate in ffmpeg output ?

  8 septembre 2011, par userffmpeg

  I have a basic doubt. In the following ffmpeg output, which of the bit rate values (in bold) tells us the video bit rate ?

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'MVI_0135.MOV' :
  Metadata :
  major_brand : qt
  minor_version : 537331968
  compatible_brands : qt CAEP
  creation_time : 2011-04-25 14:59:29
  Duration : 00:00:33.03, start : 0.000000, bitrate : 20588 kb/s
  Stream #0.0(eng) : Video : h264 (Constrained Baseline), yuvj420p, 1280x720, 19028 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 48k tbc
  Metadata :
  creation_time : 2011-04-25 14:59:29
  Stream #0.1(eng) : Audio : pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s
  Metadata :
  creation_time : 2011-04-25 14:59:29

  Its a very basic question, but I would appreciate if anyone could tell me...

• How to set a video's duration in FFMPEG ?

  1er novembre 2011, par user872387

  How to limit the video duration for a given video.For example,if we are uploading one video that should not exceed more than 5 minutes,I need a metadata in FFMPEG.Can you please find out the answer.