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Old 07-30-2020, 10:42 AM   #1
superblonde.org
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Default Adjacent AVCHD items show AV discontinuity (black frames)

I've imported into Reaper a single AVCHD file (from single recording shot) which has multiple internal MTS by converting the individual MTS files to MOV (via "AVCHD To MOV Lite" App, which uses ffmpeg internally to do the conversion) then dropping the MOV into a Reaper track ("single track" = yes).

So I have files which create 3 items :

AVCHD-00001.MOV
AVCHD-00002.MOV
AVCHD-00003.MOV

Each of the MTS files are 4.28GB (each of the MOV files are 4.08GB), because the camera split the long recording shot into these 3 segments. These segments should be 100% contiguous AV (no missing frames at beginning or end).

I notice that the item boundary shows missing data, can be seen in the screenshot below, in the audio which should be contiguous, and also, the playhead is at several black frames.




I can work around this and it may be a problem in the AVCHD-to-MOV conversion process if the TS's are not one-to-one compatible for some technical reason... So it may not be Reaper's problem... but... its a bummer. The discontinuity seems to be a little over 400 ms which is a lot.

There is also some funny business going on with Reaper because at various zoom levels, in the zero-audio part, Reaper will sometimes flicker what looks like audio data there. In general it can be seen on the screen as zero. But at some zoom levels, sometimes, it shows audio waveform, although playback always will not replay data there.

Last edited by superblonde.org; 07-30-2020 at 10:51 AM.
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Old 07-30-2020, 11:58 AM   #2
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Check this thread: https://forum.cockos.com/showthread.php?t=236950
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Old 07-30-2020, 02:09 PM   #3
superblonde.org
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These TS files are all from a single recording take and a single AVCHD file. i.e. press the camera record button, and 30 mins (or however long) later, press the stop button, the camera has made 3 files of 4GB each. It is not a combination of different items with different resolutions or sizes or frame rates etc.

Currently I'm thinking that if Reaper is having a container problem (surely, Reaper knows something is not copasetic with the item's ending frames) then it should notate that in the item name (i.e. with a "!"), or better, if Reaper is missing stream data within the container then the waveform in the timeline should show a rectangle for that area with warning text inside.
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Old 07-30-2020, 04:13 PM   #4
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Concatenate the split file segments first.

macOS/Linux
Code:
cat {00001..00003}.MTS > full_stream.mts
Windows
Code:
copy /b 00001.MTS + 00002.MTS + 00003.MTS full_stream.mts

Last edited by cfillion; 07-30-2020 at 04:20 PM.
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Old 07-30-2020, 05:50 PM   #5
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I can try that. Although if that works it would open a big mystery as to why the camera which created the AVCHD container didnt end each MTS file on a proper frame boundary or iframe or whatever it needs to end on to be "whole".
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Old 07-30-2020, 10:45 PM   #6
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It's usually a single AVCHD file split into chunks of 4 GiB minus 1 byte (~4.28 GB). That's the maximum size a file can have in the FAT32 filesystem.

Last edited by cfillion; 07-30-2020 at 10:59 PM.
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Old 08-11-2020, 06:29 PM   #7
superblonde.org
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Finally my project is complete.

It is a good suggestion and it worked 'sort of'.
i.e.
cat AVCHD-*[0-5].MTS > Big.MTS


When I dropped the Big.MTS (converted to MOV using app) into reaper adjacent to the individual 01.MOV, 02.MOV, .., etc, I notice a length mismatch. Specifically the Big.MTS is a bit shorter than all of the .mov's dropped in as 'single track'.




So I would guess that converting the small chunks to MOV introduces extra frames maybe to properly reach whatever boundary is actually correct, rather than an arbitrarily truncated file. I still wonder if Reaper can detect some funny business with MOV missing TS data to avoid this situation. I could see there was missing data (when zoomed in) so presumably Reaper should be able to detect this situation.


Anyways during later video editing in final cut using the Big.MTS I had massive problems with AV sync and had to manually adjust frames by dropping a couple at least every 1 minute, so, overall a yucky process. I realized later that if I had formatted the video camera's memory card as ExFAT then the camera would not split files into these chunks, whereas, I thought the camera would have been smart enough to behave better by default. Whether or not that would have helped the AV sync, I dont know. I should have converted to ProRes at the start.

Format SD cards to ExFAT to avoid this problem.

Last edited by superblonde.org; 08-12-2020 at 02:49 PM.
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