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• ffmpeg : remove misleading and incorrect warning messages

  15 juin 2017, par wm4

  ffmpeg : remove misleading and incorrect warning messages
  It is wrong/incorrect in two aspects :
  
  1. The pixel format is not enough to guarantee that the resulting file
  
     will be any more compatible with media players.
  
  2. Media players not supporting higher profiles are not necessarily
  
     outdated (in fact this is simply an arrogant statement that
  
     libavcodec can handle these particular features).
  You could add that there are plenty of other ways to produce widely
  
  incompatible files with ffmpeg, and these don't show any warnings.
  What we really want to do here is defaulting to codec profiles that
  
  have wide compatibility, such as main/high for h264. Also, if an
  
  encoder does not accept certain pixfmts, we should automatically
  
  convert them to a pixfmt the encoder can accept. But the existing
  
  message certainly is not appropriate.
  It also works for 2 specific encoders only. Extending it for other
  
  cases would result in a lot of special cases, so this is not the
  
  right place.
  

  • [DH] ffmpeg.c

• mp4 And Rotation - Remove Flags But Set Rotation

  7 avril 2024, par Bud

  I'm having a hard time with the rotation on some mp4 files I have. It may well be my poor understanding, so forgive me if I set out what I know (or think I know) and then what I want to happen.

  


  An mp4 has, obviously, a right way up - that is, the way you want it to show when you watch it. Call this the orientation. This isn't metadata - it's just the way you, as a person, want to see the image, with people's heads at the top of the screen and their feet at the bottom.

  


  As part of the metadata, mp4 files have a value/parameter (I believe called 'rotate') that tells how much the mp4 needs to be rotated (0, 90, 180, 270 degrees) so that it is correctly oriented. This value/parameter is observed by some players and not by some others. So if I play my video using this player, all is good (because it observes the value/parameter) - but if I play it with that other player, everything is sideways (because it doesn't observe the value/parameter).

  


  What I want to do is orient the mp4 correctly with the value/parameter set to 0, so that no matter what player plays it, it will always be played oriented correctly (because those players that observe the value/parameter will see it's 0 and do nothing). So I think what I need to do is somehow remove the value/parameter, then rotate the mp4 to the correct orientation without using the rotate value/parameter. I'm thinking of something like what FastStone Image Viewer can do with JPGs - rotate them losslessly without setting the rotate value.

  


  I've used ffmpeg and believe that it removed the rotate value/parameter (or set it to 0) because after I used it, suddenly my video appeared sideways in Windows Explorer, where previously it had appeared right way up. But how do I now rotate it to the correct orientation without changing the rotate value/parameter ?

  


  Sorry, this is very long winded and confused. Just like me.

  


• What exactly is time_base in ffmpeg ?

  29 juin 2019, par Gilgamesh22

  I have a project in which I receive frames sequentially to encode a mp4-h264 video. I also receive the timestamp in milliseconds along side the frame to indicate where in the video to place the frame. Because of this I decided to have a time_base of 10000 to simplify the placement of the frame since the frame rate is variable with an average fps of 30. I later learned that this causes problems in some video players. I was wondering if there is a proper way to accomplish this. at the moment my current solution is to set the time_base to 30 and simply set the frame->pts to timestamp of the frame divide by (10000/30).

  Original Setup

      AVCodecContext *cctx;
  
      AVStream* stream;
  
  
  
      stream->time_base.num = 1;
  
      stream->time_base.den = 10000;
  
  
  
      stream->r_frame_rate.num = 30;
  
      stream->r_frame_rate.den = 1;
  
  
  
      cctx->time_base.num = 1;
  
      cctx->time_base.den = 10000;
  
  
  
      cctx->framerate.num = 30;
  
      cctx->framerate.den = 1;

  My Questions

  1) what exactly is time_base because I always though time_base was simply a used to extract location of the frame and was abstracted away during the encoding process.

  2) what is the difference between framerate and time_base.

  3) why does a large time_base with large gaps of missing frames cause this problem in only some players.