Comment 10 for bug 503112

I spent some time looking at this bug tonight. I haven't been able to fix it, but did notice a couple of things which might be pointers to the problem.

Cutting the same video in Kdenlive does not result in white output. Comparing the xml files between Kdenlive & Openshot, there is a difference of 2 frames in the in & out points & overall length of the clip (the length in frames is reported as 1705 in melt, 1707 in Openshot). This may or may not be relevant.

While working with the clip, the line:

[mpeg1video @ 0xaf0a5640]Missing picture start code

was output occasionally, which may indicate that we are cutting in a segment that doesn't contain an I Frame - I'm not sure under what conditions ffmpeg throws out that error. Mpeg video contains I frames (key frames), P frames (predicted frames) & B frames (bi-directional predicted frames), it is not possible to playback a segment of video before the first I frame in the segment, so if we are cutting out the I frame, this would explain the white output.

I'm not sure how we can ensure the cut segment includes an I frame, or even if that is desirable, as that would result in the cut being a number of frames away from where it was intended to be (there are usually 12-15 reference frames per I frame).

More research required.