youtube-dl failing to merge formats via ffmpeg

[viticci]

After downloading separate video and audio tracks for a video via youtube-dl with the following command:

youtube-dl -f 313+251 https://www.youtube.com/watch?v=JiwIuWFLv-U

iSH fails to merge formats at the end, returning the following encoder error via ffmpeg:

[youtube] JiwIuWFLv-U: Downloading webpage                                                                                                                                                
[youtube] JiwIuWFLv-U: Downloading video info webpage                                                                                                                                     
[download] Destination: What's on my iPad Pro!-JiwIuWFLv-U.f313.webm                                                                                                                      
[download] 100% of 677.26MiB in 07:48                                                                                                                                                     
[download] Destination: What's on my iPad Pro!-JiwIuWFLv-U.f251.webm                                                                                                                      
[download] 100% of 8.06MiB in 00:05                                                                                                                                                       
[ffmpeg] Merging formats into "What's on my iPad Pro!-JiwIuWFLv-U.webm"                                                                                                                   
ERROR: Unknown encoder 'copy'

For context, here is the successful output for the same command from macOS:

[youtube] JiwIuWFLv-U: Downloading webpage
[youtube] JiwIuWFLv-U: Downloading video info webpage
[download] Resuming download at byte 85454848
[download] Destination: What's on my iPad Pro!-JiwIuWFLv-U.f313.webm
[download] 100% of 677.26MiB in 01:23
[download] Destination: What's on my iPad Pro!-JiwIuWFLv-U.f251.webm
[download] 100% of 8.06MiB in 00:01
[ffmpeg] Merging formats into "What's on my iPad Pro!-JiwIuWFLv-U.webm"
Deleting original file What's on my iPad Pro!-JiwIuWFLv-U.f313.webm (pass -k to keep)
Deleting original file What's on my iPad Pro!-JiwIuWFLv-U.f251.webm (pass -k to keep)

[cliss]

To my eyes, based on nothing but a hunch, this has nothing to do with youtube-dl and everything to do with ffmpeg. (@viticci implied this above.)

For the life of me, I can't understand how the copy coder couldn't be available, and nothing that's unique to iSH should cause an error like this.

Furthermore, I did a cursory search of the ffmpeg repo to see if I could find the string Unknown encoder but came up short.

The best I can guess is that there is some sort of deeper error which is being reported as a missing encoder...? ¯\(ツ)/¯

[Drvolks]

You’re right it’s a ffmpeg issue.

ffmpeg -i video.mp4 -i audio.m4a -c:v copy -c:a copy output.mp4

Will result in the same « Unknown encoder 'copy' » error.

-loglevel debug doesn’t reveal any hint on the underlying issue:

Successfully opened the file.                                                                                                                          
Parsing a group of options: output url output.mp4.                                                                                                     
Applying option c:v (codec name) with argument copy.                                                                                                   
Applying option c:a (codec name) with argument copy.                                                                                                   
Successfully parsed a group of options.                                                                                                                
Opening an output file: output.mp4.                                                                                                                    
Unknown encoder 'copy'            

[tbodt]

This smells like some kind of subtle CPU bug that takes a day to debug and is fixed by changing 1 character.

[tbodt]

I just tried ffmpeg on the "you've been gnomed" video and it seems to be working now. Maybe there was an ffmpeg update? Maybe it's only broken on aarch64? (likely)

[cliss]

Just apk del’d everything and then re-added it, and still can’t use the copy encoder.

So weird.

[tbodt]

It's definitely an arm64-specific CPU bug, it doesn't work on iOS but it does work on my computer

[tbodt]

Fixed now, it was a screwup in 8-bit string compares.

[cliss]

@tbodt

1. Thanks!! Stoked to try it!!
2. Purely out of curiosity, was 5b4807c the commit that fixed it?
3. # setting flags: a horror story 🤣 you write comments like I do

[tbodt]

Yup, 5b4807c was the fix. Checking overflow on 8-bit subtraction on arm64 is the third hard problem in computer science.

[cliss]

Hahahahahahahaha 🤣🤣🤣

[cliss]

Excuse me for being a bit over enthusiastic, but...

OMFG IT WORKS AND IT’S SO DAMN FAST LOOK AT THIS

frame= 2844 fps=221 q=-1.0 Lsize=  257424kB time=00:01:34.84 bitrate=22233.7kbits/s speed=7.38x