Video showing black in timeline and on export

Lillian-Fidler wrote on 12/12/2023, 3:50 PM

Hi, This is a strange one. I have a project that is about 2 hours long. There are many imported pieces of video that make up the 2 hours. Everything is perfect, except for this one .mp4 file, which is about 15 minutes long. I tried opening it in it's own project as well, but it's mostly black. It starts out fine, but most of it is just black. The properties are in the attached screenshot. Any ideas on what I can do here?

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CubeAce wrote on 12/13/2023, 2:13 PM

@Lillian-Fidler

That is a trickier one to answer.

Some people like all their files for a project in it's own folder along with the videos and images. Others prefer to just have the editing data in a folder and leave the videos and images where they are, especially if they use some videos and images in different projects.

All I would say is it is best to have the C: drive purely for programs. Any other data should be kept on a separate drive. Internal fast drives are preferable to external drives where possible.

He are mine, hopefully to be updated as some need data transferred and replaced. Only the F drive is external.

Ray.

johnebaker wrote on 12/13/2023, 3:58 PM

@Lillian-Fidler

@browj2 commented:

. . . It would be good to find out the source of the video and how it got the way it is to make sure that you get a better file next time...and for whoever produced it to improve their process. . . .

I agree wholeheartedly with this.

For future contributions from others, I would advise you to ask for the original recording, or if the recording has been compiled by them, it must be a short GOP version, ie no longer than the framerate of the video, eg if the framerate is 30 fps than the GOP length should be no longer than 30.

The file has definitely been through a video converter such as Handbrake, Xmedia Recode or another FFmpeg based converter to convert to long GOP,

The clue was this line from MediaInfo data analysis which is the 'signature' for FFmpeg

Writing library : x264 core 140 r2377 1ca7bb9

For direct streaming, IMHO, a GOP length of 250 is too long, I use a GOP length of 100 maximum for video at 25fps, at 30 fps I would use a maximum value of 120.

HTH

John EB

AAProds wrote on 12/13/2023, 5:07 PM

@johnebaker

John, how are you determining the GOP?

AAProds wrote on 12/13/2023, 5:17 PM

I'm not sure that the GOP is the issue here. The second file I sent Lillian also had a GOP of 250 (as far as I can tell; there is 10 seconds between I-frames at 25fps in AVIDemux); that file worked OK.

johnebaker wrote on 12/14/2023, 6:37 AM

@AAProds

Hi Al

. . . . how are you determining the GOP . . . .

Using Bitrate Viewer in Frame mode.

Each vertical line above 15000 is an I frame those below are P & B frames, a quick scan with the moving the cursor shows these are 250 frames apart.

. . . . there is 10 seconds between I-frames at 25fps in AVIDemux . . . .

That gives the GOP length: 25fps x 10s = 250.

When looking at GOP structure there are 2 parameters - M and N. MediaInfo will usually tell you these values for GOP based video, it is interesting that MediaInfo does not give this info on the sample video provided

M = distance between two 'anchor' frames (I or P)

N = distance between two I frames

For a GOP of M=3, N=13

The sequence is IBBPBBPBBPBBPI for one GOP

As you can see, counting from the first I frame, the P frames are at positions 3, 6, 9 and 12 , ie the spacing is the M parameter.

The BBP sequence continues until N frames have been reached, where a new I frame is created and so on until you reach the end of the video clip.

Interesting side note - my first Sony camera, bought in Sydney in 2006, always had a single P frame before the first I frame of the first full GOP. I assume that many other cameras also do this, as MMS/MEP/VPX has a Crop option in the program settings there is a to take care of this on import.

John EB