The following are a list of ffmpeg conversions that QuickTime 3 for 
System 7 seems to support; however, these were tested via the 
"Basilisk II" emulator.

Last updated: 2025/05/25

The 'rpza' version results in an EXTREMELY LARGE file.

The 'cinepak' version is insanely slow to convert to but has the best 
resulting frame-rate. However, the file-size will still be large but not
as high as 'rpza'; about 600-700MB for a 20ish minute video. You can 
speed-up conversion by adding "-r 15 -s 320x240" to shrink the 
size and fps. Cinepak is also a format used in Sega Saturn videos.

The 'mjpeg' version has a terrible frame-rate.

SVQ1 is "Sorenson Video." This will 10-20x the video-size of a standard 
H264 MP4 when converting to MOV. The frame-rate is about as good as the
'cinepak' video codec.

ffmpeg -hide_banner -threads 0 -i "input.mp4" -vf 'scale=trunc(oh*a/2)*2:480' -c:v rpza -b:v 600k -maxrate 600k -ar 22050 -c:a adpcm_ms -passlogfile "/tmp/ffmpeg.log" -pass 1 "output.avi";
ffmpeg -hide_banner -threads 0 -i "input.mp4" -vf 'scale=trunc(oh*a/2)*2:480' -c:v cinepak -b:v 600k -maxrate 600k -ar 22050 -c:a adpcm_ms -passlogfile "/tmp/ffmpeg.log" -pass 1 "output.avi";
ffmpeg -hide_banner -threads 0 -i "input.mp4" -vf 'scale=trunc(oh*a/2)*2:480' -c:v mjpeg -b:v 600k -c:a adpcm_ms -ar 22050 -passlogfile "/tmp/ffmpeg.log" -pass 1 "output.mov";
ffmpeg -hide_banner -threads 0 -i "input.mp4" -vf 'scale=trunc(oh*a/2)*2:480' -c: svq1 -b:v 600k -maxrate 600k -c:a adpcm_ms -ar 22050 -passlogfile "/tmp/ffmpeg.log" -pass 1 "output.mov";

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According to https://welcometomacintosh.neocities.org/notes ...
(All of this was copied/pasted, so "my" does not actually mean "me")

* ffmpeg's implementation of quicktime ima4 audio compression crashes 
  quicktime with a type 3 (QT 2.5.1) or type 4 (QT 4.0.3) error. So 
  we're stuck with sowt, which means to acheive similar compression from
  a 16-bit 44100Hz stereo source, we have to half the bit depth and the 
  sampling rate to 8 and 22050 respectively, as well as converting 
  to mono. If ima4 wasn't broken we could have 16-bit 22050Hz stereo 
  audio.
  
* In my tests, a 68k macintosh can not reliably play back anything 
   better than 320x240@15p.
    
* For HD video this means our target resolution is 320x180p.

 Here's the video filter line I used:

vproc="pp=ac,pp=ac,pp=ac,hqdn3d=5,eq=contrast=256/220:brightness=1/512:saturation=256/224:gamma=16/16,scale=320:-4:sws_flags=spline+accurate_rnd+full_chroma_int+full_chroma_inp:sws_dither=2:in_range=0:out_range=2,minterpolate=fps=15:mi_mode=mci:me_mode=bidir:me=ntss:vsbmc=1,xbr=2,format=pix_fmts=rgb24"

And the audio filter line:

pan=mono|FC < 1.414FC+FR+FL+0.5BL+0.5SL+0.25LFE+0.125BR,aresample=resampler=soxr:osr=22050:cutoff=0.990:dither_method=shibata

And finally the command line, with the filters chains in the proper places.

    ffmpeg -v 32 -stats -y -i <filename> -vf <video filters> -c:v cinepak -q:v 30 -af <audio filters> -c:a adpcm_ima_qt -f mov <output filename>

Because ffmpeg's cinepak encoder is absurdly slow and mostly only exists
so they can claim they can do it, rather than as a practical tool, 
expect this to render at approximately 0.2x realtime. A faster method 
would be to scale your HD content down on a modern PC, encode to prores 
as an intermediate, and then sneakernet it to an old G3 or G4 macintosh 
to do the encoding directly with quicktime. You could probably approach 
2x or 3x realtime using this method, ffmpeg's encoder is that bad. (This
also has the added bonus of allowing you to use ima4 for your audio, 
giving you somewhat higher quality.)

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Also see http://synack.net/~bbraun/68kvideo.html