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Some tutorials online recommend converting a video to an image sequence in Blender before using the motion tracking features. See https://www.youtube.com/watch?v=InIuTtt7W3E?t=135, which explains that doing it directly to a video works but does not save correctly i.e. next time you re-open the project you'll find the video is out of sync.

I find this hard to believe, that something as simple as this is broken in Blender.

Can anyone elaborate on why this is the case with Blender?

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You don't necessarily have to convert video to an image sequence.

Blender is not broken, but can only work with video that is encoded with certain specific parameters.

Video encoded with intraframe will work fine. All of the information in each frame is independent of the previous or following frames (same as with an image sequence)

Video encoded with interframe compression will likely yield errors, since the information needed to decode each frame is dependent on adjacent frames and only the differences are calculated.

Also, if the video is encoded using any kind of variable framerate, it needs to be re-encoded to a uniform framerate before being imported in blender. Blender will not do on-the-fly framerate conversion or temporal interpolation in any way.

Read: http://www.leckman.com/articles/codecs_05.html

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    $\begingroup$ Even if your system did support any compression, youd most likely want to convert the footage to something more suitable to random lookup. The cost is minimal, but the benefits are huge. $\endgroup$ – joojaa Dec 31 '19 at 7:59
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    $\begingroup$ Part of the issue is that non-professional cameras (phone cameras, for example) use delivery codecs (8 bit, long GOP, variable framerates) to create small files. Those files are designed to minimize file size and facilitate playback at the expense of precision. They are a poor choice for precision editing and any form of post-production. Professional cameras use production codecs or raw files, that will yield much larger files, with less compression, more bits per pixel and stable framerates. Only after post-production those images are converted to delivery codecs for easy playback. $\endgroup$ – user1853 Dec 31 '19 at 17:18

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