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• ffmpeg FPS information mismatch with the video

  8 décembre 2017, par Adorn

  I have a bunch of videos with some statistics of what is happening inside a video. One such piece of information is given in terms of time of the video in seconds up to one decimal point.

  To get the FPS of a video, I am using ffmpeg -i

  But when I manually compute one particular frame’s time using given FPS, it does not match.

  For example, ffmpeg outputs FPS = 30.

  I look at the video statistics, the frame at the 156.8 = 2.368 has to be
  4704'th frame. I open the video using ’skvideo’, read all the frames, and view the 4704'th frame. It is some frame around time 2.12 ?. I checked multiple such instances in multiple videos and this is a common behavior.

  I do not understand why this is so and how can I get around the problem ?

  As such I am not bounded by ffmpeg. Skvideo is being used to read the videos. I tried opencv, as of now it does not work with VideoCapture, and reinstalling it is costly for me time wise. But I guess ’opencv/skvideo’ should not matter, one can count the frames manually as well.

  So, in the solution, I am looking out for -

  1. Given timestamps of inside of a video, how can I find a frame of that particular time location ?

  2. In case someone might have already worked on this, this is related to THUMOS dataset. I am on Ubuntu 16.04

  EDIT_1

  Actually I can be more specific as it is a publicly available data. The time bounds are of an important activity. For example, in a video, when does basketball dunk occurs ? It is given in pairs - [start end]. Some videos have multiple activities, some have only one.

  Here is a sample video, and following are the activity times.

  [[  16.5, 20.8],
  
  [  26.6, 32.2],
  
  [  34.8, 42.1],
  
  [  47.8, 50.0],
  
  [  58.1, 62.9],
  
  [  65.6, 67.2],
  
  [  68.5, 74.0],
  
  [  76.4, 78.3],
  
  [  78.7, 79.8],
  
  [  80.8, 82.1],
  
  [  85.0, 87.3],
  
  [  90.1, 91.4],
  
  [  98.5, 100.3]]

  I also tried checking manually, 32.87 FPS "almost" works for few videos but not for all. and almost means it is off by 10 frames. This is a huge difference for my task, and I need exact frame.

  Also, there has to be some way, because it can be visually observed with multiple video players that times in the dataset are correct.

• avcodec/dnxhddec : Do not overwrite colorspace if the container has set it.

  29 novembre 2017, par Steven Robertson

  avcodec/dnxhddec : Do not overwrite colorspace if the container has set it.
  The existing logic overrides container metadata even in cases where the
  
  container metadata must be trusted (e.g. HDR). The original spec had no
  
  provision for specifying color volume, so many files rely on the
  
  assumption of Rec. 709.
  An update to the spec included a 'clv' field for explicitly signaling
  
  that the container should be trusted in an existing bitfield in the
  
  frame header, but the default of 0 from old encoders forces Rec. 709,
  
  which would break any HDR stream. Because there is no place in DNxHR for
  
  specifying a transfer function, DNxHR HDR files must include
  
  container-level color information.
  This patch maintains the existing behavior of choosing the 709 over the
  
  601 matrix when container-level information is missing, and allows
  
  container-level information to win if present.
  Signed-off-by : Steven Robertson <steven@strobe.cc>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/dnxhddec.c

• hwcontext_vaapi : Do not assume that sw_format is transferable

  24 novembre 2017, par Mark Thompson

  hwcontext_vaapi : Do not assume that sw_format is transferable
  Drivers can support a format for surfaces without also supporting it for
  
  images, so we can't assume that sw_format is usable for transfer.  This
  
  would previously hit an assert in cases where it isn't.
  

  • [DH] libavutil/hwcontext_vaapi.c