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Quicktime Reference Will Not Decode Properly

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John Michaels
Quicktime Reference Will Not Decode Properly
on Jun 23, 2014 at 4:40:20 am

Hello! I have never been able to get ffmpeg to decode Quicktime reference files properly. Usually ffmpeg will only read to the first "edit point," and then stop there.

Steps to reproduce:

- Take two self-contained Quicktime files of the same codec, test that they will be decoded by ffmpeg. I typically use XDCAM or ProRes Quicktimes, but this goes for any MOV.
- Now import them into Final Cut Pro, splice a few segments from both sources together in a Sequence. Maybe add a transition or something, so that the output MOV will have some rendered content.
- Export that Sequence as Quicktime, do not check "Self Contained," so that the source files are referenced.
- Now try to use ffmpeg to decode/transcode the output MOV to something else. You will not end up with the complete video.

I've noticed if you try to play a Quicktime Reference in VLC, you will see a very similar phenomenon. Presumably because VLC and ffmpeg both use libavcodec?

Does anybody know of a fix for this? I am unsure what exactly the problem is. Could ffmpeg be failing to resolve the paths to the referenced files? Or does it choke at the next rmra atom?


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Reuben Martin
Re: Quicktime Reference Will Not Decode Properly
on Jun 30, 2014 at 4:58:24 pm

I may be wrong, but I believe the problem with doing it this way is that the data streams are pulled directly from the reference files, which means timestamps (PTS and DTS) jump around whenever the source changes. FFmpeg is an encoder, not an editor, and it expects continuity in the timestamps.

There may be other reasons though. Really you shouldn't try to use Quicktime Reference outside of software built using the Quicktime API.


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John Michaels
Re: Quicktime Reference Will Not Decode Properly
on Jun 30, 2014 at 5:05:44 pm

Thank you for the insight. I was thinking it was an issue resolving the paths of the referenced files, but the timestamp issue makes sense, too. However, shouldn't flags such as +genpts and +ignoredts solve this issue? In my experience, setting these flags does not solve the issue.


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Reuben Martin
Re: Quicktime Reference Will Not Decode Properly
on Jun 30, 2014 at 9:31:13 pm

I don't think those flags entirely do what their names would imply. I've run into timestamp issues multiple times and those flags have done little to fix the problem. A quick web search will reveal mailing lists littered with problems related to FFmpeg and DTS / PTS timestamp issues.


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