FFMPEG fast frame count #1004
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FFMPEG fast frame count #1004
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Instead of advancing through the entire video and counting every frame, the new algorithm seeks to the last keyframe it can find and then advances to the end to discover the frame number of the last frame. With this change the number of frames is accessible in constant time rather than linear in the number of frames of video.
chetnieter
approved these changes
Jun 1, 2020
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This is one last feature I'd like to get into KWIVER before the next release. This change allows FFMPEG to provide an accurate frame count quickly (in constant time) without scanning the whole video. Since we are now trusting the accuracy of seeking we can seek to the last key frame and advance to the end to find the last valid frame. There are existing tests that compare the output of
num_frames()to a count of frames by stepping through all frames. These tests continue to pass. I've also validated that the frame counts are accurate on several real videos.This change allows us to open very large videos in TeleSculptor in seconds without waiting minutes or hours to scan the whole video.