compression - finding a keyframe in mdat -


A QuickFilter document recommends the following approach to search a keyframe:

Finding Key Frames

Searching for a significant frame for a specified time in the film is slightly more complex than finding a sample for a specified time. Media handlers need to use sync sample atoms and time-per-sample atoms to find key frames.

The Media Handler follows these steps:

  1. Examines the time-to-sample atom to determine the sample number, which contains the data for the specified time is.
  2. Scan sample atom to scan key to find the key frame before the sample number selected in step 1.
  3. In which frame scans the sample-to-chak molecule to detect the key?
  4. Makes offsets off of offset offset offs
  5. Sample size uses the atom to find the offset of the chuck and sample size. Source:

    Source:

    This is quite confusing because many tracks ("trunk" atom) will produce different offsets. For example, the keyframe-sample-chuck-offset value for the video track would be a value, and the audio would be another.

    Any file located above the instructions in the file (or Mdat atom)?

It is not limited to main frames. You can not guarantee that different tracks in the file The samples are close to each other. You hope that audio and video will be duplicated so that you can play back the movie without excessive demand, but it depends on the software that created the file. Each track has its own sample table and chola atom, which tells you where samples are in the file and they can be anywhere. (They may also be in a separate file, although reference movies are now deprecated so that you can ignore them.)


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