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Transcoding and re-linking glitchy media
Hi All! I’ve got some footage that was shot UHD 59.94 FPS mp4 on a GH5. Prior to bringing everything into FCPX, I had transcoded everything to ProRes 422 Proxy files. Now that the edit is mostly done, I’m am now in the process of trying to reconnect all the media to the originals.
<font face=”inherit”>When I try and </font>reconnect to the original .mp4 MOV files, FCPX gives me a ‘File could not be relinked due to same media type, length or # of audio channels’ error. Confusing to say the least since all clips are the same length as the proxies, and audio is 2 channel PCM 48khz (passthrough) in both. I then went ahead and (at great storage cost) re-rendered all clips to ProRes422 HQ using Compressor, and that *mostly* worked.
My gremlin now is that there are 6 or 7 of the reconnected ProRes 422 clips that have huge stuttering/frame geometry distortions, and are unusable. When I go back and play the original files in Quicktime or VLC, there are some barely noticeable stutters in the playback, but not any other geometry or frame distortions. Unfortunately, I can’t re-link to these in FCPX for whatever reason.
I’ve tried re-rendering the clips from source-> ProRes422 HQ in both Compressor and Adobe Media Encoder, and the result is always the same.
My next step was to try and render the clips as high quality Photo JPEG, and those re-link and playback in FCPX seemingly fine, but I’m worried that having unmatched media in that codec will cause problems with color correction.
I’ve googled around a bit looking for solutions to the re-linking fail, but haven’t found anything on really point. Does anyone have some wisdom to share on how to save glitchy clips in a way that preserves the original fidelity?
Thanks!
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1 Reply
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In general it is risky to use externally-generated proxies as original media then plan on relinking to the true original media. It’s true this can be done and some people use camera-generated proxies. However it requires *lots* of testing before committing to this workflow.
For most users it is far better to use the built-in FCPX proxy system, which now supports various frame sizes, H264, and proxy relinking.
However starting with 10.4.9 there is apparently an undocumented method of using XML to connect externally-generated proxies to FCPX as actual proxies (not original media). Apple mentioned this when 10.4.9 was released, describing it this way:
“Editors can now link to proxy media generated by third-party applications via XML. Examples include Frame.io, a cloud-based creative collaboration platform for review and approval, plus asset management tools like Keyflow Pro and PostLab.”
To my knowledge public documentation about how to construct that XML does not exist. Those details must be privately held between Apple and a few approved companies.
If you pick a *single* proxy file and try to relink that, the dialog will tell you the reason it fails. It won’t do this when relinking multiple files.
Once you do that for one file, note the reason it fails. Then use Invisor’s comparison mode to examine the metadata of your proxy and the original file, and see where they differ.
https://apps.apple.com/us/app/invisor-media-file-inspector/id442947586?mt=12
Some relink issues can be solved by deleting all FCPX cache files, which includes thumbnails. That cannot be done with the FCPX UI but only by deleting the folders within the library. The safest approach is use the Library Inspector Storage Locations>Modify Settings>Cache to define a folder for cache. That places all cache items including render cache, optical flow, waveforms and thumbnails in a single bundle named YourLibraryName.fcpcache. You can safely shut down FCPX, delete that entire bundle, re-launch FCPX and the items will be regenerated. Note there is a bug on FCPX before 10.4.10 on Catalina whereby it will hang if attempting to create a folder using that UI. That is fixed in 10.4.10.
Since you apparently have relinked most of the clips and have a problem on a few, you may need to manually do a replace edit on those clips then copy/paste the attributes. You can usually use the clip skimmer to find the starting clip timecode of the current clip in the timeline, note the clip length, then find the corresponding range in the original media clip, mark that range then do OPT+R to replace.
Known FCPX re-link constraints:
– Files must have the same audio config (same number of channels), but sample rate can differ.
– Pixel aspect ratio should be the same, but it may relink even if different. This could result in a squeezed or stretched frame.
– Clip duration must be the same or longer. If longer, then later relinking to the original clip won’t work because the new target will then be shorter.
– File suffix must be the same.
– Codec need not be the same, e.g. you can create 720p H264 proxies and relink to those as original media.
– After relinking to a different resolution file, the viewer may show a window-boxed screen. This is typically a cache issue and can be resolved by deleting the FCPX cache for that event, which is either stored in the library or outside as defined by the library inspector. The cache is a file bundle named LibraryName.fcpcache.
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