SET filters="fps=%4,scale=%3:-1:flags=lanczos"
  ffmpeg -v warning -i %1 -vf "%filters%,palettegen" -y palette.png
  ffmpeg -v warning -i %1 -i palette.png -lavfi "%filters% \[x\]; \[x\]\[1:v\] paletteuse" -y %2
  DEL palette.png

  togif.bat <input.mp4> <output.gif> <width> <fps>

  ffmpeg -i "path\to\my_input_video_file.mp4" "path\to\my_output_audio_only.wav"

  ffmpeg -i "path\to\my_input_video_file.mp4" -map 0:0 -c copy video.mp4 -map 0:1 -c copy audio0.m4a -map 0:2 -c copy audio1.m4a

  (echo file 'first file.mp4' & echo file 'second file.mp4' )>list.txt
  ffmpeg -safe 0 -f concat -i list.txt -c copy output.mp4

  ffmpeg -i input -c:v libx264 -crf 18 -c:a copy output.mkv

  ffmpeg -i input -c:v libx265 -vf format=yuv420p -c:a copy output.mkv

  ffmpeg -i input -c:v libx264 -crf 18 -vf format=yuv420p -c:a copy output.mkv

    ffmpeg -hwaccel cuvid -c:v h264_cuvid -i input.mp4 -vf "hwdownload,format=nv12,scale=(iw*sar)*max(1280/(iw*sar)\,720/ih):ih*max(1280/(iw*sar)\,720/ih), crop=1280:720, subtitles=input.srt:force_style='FontName='TiresiasScreenfont',Fontsize=32,Outline=2,MarginL=50,MarginV=30,Alignment=1',minterpolate=fps=60:mi_mode=blend" -c:v h264_nvenc -preset slow -b:v 8M -f matroska - | vlc -

For me I want subtitles with Tiresias screen font used in Finnish YLE 90s. (Aligned always to left second row, so that starting point is always the same. Center alignment is bad because you need to always re-adjust eyes to the position where the subtitles start, left alignment makes the first character always in same place.)

* `hwaccel cuvid -c:v h264_cuvid` * makes the hardware accelerated decoding (h264 only)

* `-vf` * video filter

* `hwdownload,format=nv12` * downloads the hardware accelerated frame to memory for the video filter (required by cuvid)

* `scale=(iwsar)max(1280/(iwsar)\,720/ih):ihmax(1280/(iw*sar)\,720/ih), crop=1280:720` * crops the video to 1280x720, (exteremely high impact on performance!) Use crop and resize cuvid below for better performance.

* `subtitles=input.srt:force_style='FontName='TiresiasScreenfont',Fontsize=32,Outline=2,MarginL=50,MarginV=30,Alignment=1'` * subtitles

* `-c:v h264_nvenc -preset slow -b:v 8M` * hardware accelerated encoding 8000 kb/s for 720p/60 (for 1080p use `16M`)

* `-f matroska * | vlc -` * output as matroska, pipe to VLC

* `minterpolate=fps=60:mi_mode=blend` * output 60 fps interpolate blending (this can cause problems, avoid sometimes)

Crop and resize with cuvid example:

* `-hwaccel cuvid -crop 0x0x200x200` - faster way to crop top x bottom x left x right

* `-hwaccel cuvid -resize 1200x300` - resize (forces the size)

Seek example:

Seek to 30 minutes (60*30 = 1800)

   ffmpeg -ss 1800 ... vf "hwdownload,format=nv12,setpts=PTS+1800/TB,subtitles='...',setpts=PTS-STARTPTS"`

Print subtitles (useful for old TVs that can't select a subtitle from streams or files; I use this to get my kids to watch movies in English):

    -vf "ass=subtitle.ass"

    -vf "subtitles=subtitles.srt:force_style='Fontsize=36,PrimaryColour=&H0000FFFF'"

    -vf "select='lt(mod(t,90),1)',setpts=N/FRAME_RATE/TB" -af "aselect='lt(mod(t,90),1)',asetpts=N/SR/TB"

  h264:
  -c:v libx264 -preset medium -crf 22

  h265:
  -c:v libx265 -preset medium -crf 26

  no recompress:
  -c copy

  presets:
  ultrafast,superfast, faster, fast, medium, slow, slower, veryslow

  desinterlace:
  -vf yadif

  target size:
  -s 1920x1080

  aspect ratio without recompressing:
  -aspect 16:9

  rotate video:
  -vf "transpose=1"
  0 = 90CounterCLockwise and Vertical Flip (default)
  1 = 90Clockwise
  2 = 90CounterClockwise
  3 = 90Clockwise and Vertical Flip

  rotate without recompressing:
  -metadata:s:v rotate="90"

  audio aac two channels:
  -c:a aac -b:a 160k -ac 2

  web fast start:
  -movflags +faststart

  autoscale to WxH with black bands:
  -vf "scale=W:H:force_original_aspect_ratio=decrease,pad=W:H:(ow-iw)/2:(oh-ih)/2"

  get jpeg snapshot:
  -vframes 1 -q:v 2 dest.jpg

  concatenate mp4 without recompressing:
  -f concat -safe 0 -i "files.txt" -c copy -movflags +faststart
  files.txt format:
  file 'filepath'

  ffprobe get videoinfo:
  ffprobe -v quiet -print_format xml -show_format -show_streams "filepath" > file.xml

  if override which sub track is default, use "-default_mode infer_no_subs"

  clear disposition (default sub):
  -disposition:s 0

  default or forced disposition:
  -disposition:s forced

  track metadata (audio):
  -metadata:s:a title="xx"
  track metadata (video):
  -metadata:s:v title="xx"
  global metadata:
  -metadata title="xx"
  -metadata description="xx"
  -metadata comment="xx"

  extract sound from video to mp4
  ffmpeg -i source_video.avi -vn -ar 44100 -ac 2 -ab 192k -f mp3 sound.mp3

  skip time (place after input file):
  -ss 00:05:00

  stop after:
  -t 00:05:00 

  Approx fast seek (place before input file):
  -ss 00:05:00 -noaccurate_seek -i ....

    ffmpeg -i 'input.mkv' -filter_complex '[0:a:1]volume=0.1[l];[0:a:0][l]amerge=inputs=2[a]' -map '0:v:0' -map '[a]' -c:v copy -c:a libmp3lame -q:a 3 -ac 2 'output.mp4'

  ffmpeg -hide_banner -loglevel error -nostdin -y -i "$f" -map 0:0 -c:v copy -map 0:a:0? -c:a:0 aac -b:a:0 160k -filter:a:0 "pan=stereo|FL=1.414*FC+0.707*FL+0.5*FLC+0.5*BL+0.5*SL+0.5*LFE|FR=1.414*FC+0.707*FR+0.5*FRC+0.5*BR+0.5*SR+0.5*LFE,acompressor=ratio=4" -metadata:s:a:0 title="NightMixed" -metadata:s:a:0 language=eng -disposition:a:0 default -map 0:a:0? -c:a:1 copy -disposition:a:1 none -map 0:a:1? -c:a:2 copy -disposition:a:2 none -map 0:a:2? -c:a:3 copy -disposition:a:3 none -map 0:a:3? -c:a:4 copy -disposition:a:4 none -map 0:a:4? -c:a:5 copy -disposition:a:5 none -map 0:a:5? -c:a:6 copy -disposition:a:6 none -map 0:a:6? -c:a:7 copy -disposition:a:7 none -map 0:a:7? -c:a:8 copy -disposition:a:8 none -map 0:a:8? -c:a:9 copy -disposition:a:9 none -map 0:s:0? -c:s:0 copy -map 0:s:1? -c:s:1 copy -map 0:s:2? -c:s:2 copy -map 0:s:3? -c:s:3 copy -map 0:s:4? -c:s:4 copy -map 0:s:5? -c:s:5 copy -map 0:s:6? -c:s:6 copy -map 0:s:7? -c:s:7 copy -map 0:s:8? -c:s:8 copy -map 0:s:9? -c:s:9 copy "/home/pi/media/remixed_in_progress/$f"

    ffmpeg -i source.avc -c copy -bsf:v h264_metadata=colour_primaries=1:matrix_coefficients=1 output.h264

  function grab-screen-lossless {
    ffmpeg -an -f x11grab -video_size 1920x1080 -framerate 60 -i :0.0 -c:v h264_nvenc -preset llhq -tune zerolatency -crf 0 -qp 0 "${1}"
  }
  
  function grab-screen {
    ffmpeg -an -f x11grab -video_size 1920x1080 -framerate 60 -i :0.0 -c:v h264_nvenc -preset llhq -tune zerolatency -qp 10 "${1}"
  }
  
  function vid_compress {
    ffmpeg -i "${1}" -codec:v libx264 -preset:v fast -pix_fmt yuv420p "${2}"
  }

  # 1. Record your device using QuickTime 
  #  (File->New Movie Recording->Select your phone)
  # 2. Run `$ app-preview your-recording.mov`

  function app-preview() {
      echo "name $1"
      ffmpeg -i $1 -vf scale=1080:1920,setsar=1 -c:a copy "out_$1"
  }

#!/bin/bash

#Creates a Directory

mkdir -p titles

#loop for files in folder

for f in .MOV; do

    text="${f%.MOV}"     
               

    ffmpeg -i "$f" -vf drawtext="fontfile=/usr/share/fonts/opentype/NotoSansCJK-Regular.ttc  : \

length=$(echo "$duration" | awk '{ split($1, A, ":"); print 3600A[1] + 60*A[2] + A[3] }' )

trim_start="$2"

trim_end=$(echo "$length" - "$3" - "$trim_start" | bc)

ffmpeg -ss "$trim_start" -i "$1" -c copy -map 0 -t "$trim_end" "./trimmed/$1"

# Example # >trim example.MOV 0.2 10

  # Save a RTSP stream to file
  ffmpeg -i rtps://someserver/somevideo -c copy out.mp4

  # encoding quality settings examples
  #   H264
  ffmpeg -i input.mp4 -a:c copy -c:v libx264 -crf 22 -preset slower -tune film -profile:v high -level 4.1 output.mp4
  #   H264 10bit (must switch to a different libx264 version)
  LD_LIBRARY_PATH=/usr/lib/x86_64-linux-gnu/x264-10bit ffmpeg -i input.mp4 -a:c copy -c:v libx264 -crf 22 -preset slower -tune film -pix_fmt yuv420p10le -profile:v high10 -level 5.0 output.mp4

  # resize 
  ffmpeg -i in.mp4 -s 480x270 -c:v libx264 out.mp4

  # change source fps
  ffmpeg -r 10 -i in.mp4 out.mp4

  # resample fps
  ffmpeg -i in.mp4 -r 10 out.mp4

  # extract the audio from a video
  ffmpeg -i inputfile.mp4 -vn -codec:a copy outputfile.m4a

  # merge audio and video files
  ffmpeg -i inputfile.mp4 -i inputfile.m4a -codec copy outputfile.mp4

  # cut (reencoding)
  #   set the start time and duration as HH:MM:SS
  ffmpeg -ss 00:00:40.000 -i input.mp4 -t 00:00:10 -c:v libx264 output.mp4
  #   set the start time and duration as seconds
  ffmpeg -ss 40.0 -i input.mp4 -t 10.0 -c:v libx264 output.mp4
  #   skip an exact number of frames at the start (100)
  ffmpeg -i input.mp4 -vf 'select=gte(n\,100)' -c:v libx264 output.mp4

  # cut (w/o reencoding - cut times will be approximate)
  ffmpeg -ss 40.0 -i input.mp4 -t 10.0 -c copy output.mp4

  # save all keyframes to images
  ffmpeg -i video.mp4 -vf "select=eq(pict_type\,I)" -vsync vfr video-%03d.png

  # encode video from images (image numbering must be sequential)
  ffmpeg -r 25 -i image_%04d.jpg -vcodec libx264 timelapse.mp4

  # flip image horizontally
  ffmpeg -i input.mp4 -vf hflip -c:v libx264 output.mp4

  # crop and concatenate 3 videos vertically
  ffmpeg -i cam_4.mp4 -i cam_5.mp4 -i cam_6.mp4 -filter_complex "[0:v]crop=1296:432:0:200[c0];[1:v]crop=1296:432:0:200[c1];[2:v]crop=1296:432:0:230[c2];[c0][c1][c2]vstack=inputs=3[out]" -map "[out]" out.mp4

  # 2x2 mosaic (all inputs must be same size)
  ffmpeg -i video1.mp4 -i video2.mp4 -i video3.mp4 -i video4.mp4 -filter_complex "[0:v][1:v]hstack=inputs=2[row1];[2:v][3:v]hstack=inputs=2[row2];[row1][row2]vstack=inputs=2[out]" -map "[out]" out.mp4

  # picture-in-picture
  ffmpeg -i video1.mp4 -i video2.mp4 -filter_complex "[1:v]scale=iw/3:ih/3[pip];[0:v][pip]overlay=main_w-overlay_w-20:main_h-overlay_h-20[out]" -map "[out]" out.mp4

  # print framerate of every file in dir
  for f in *.mp4; do echo $f; mediainfo $f|grep "Frame rate"; done

  # print selected info of every file in dir in CSV format
  for f in *.mp4; do echo -n $f,; mediainfo --Inform="Video;%Duration%,%FrameCount%,%FrameRate%" $f; done

    fd -t f -e flac . "$@" -x ffmpeg -loglevel 16 -i "{}" -qscale:a 0 "{.}.mp3"

  ffmpeg -f lavfi -i testsrc=d=60:s=1920x1080:r=24,format=yuv420p -f lavfi -i sine=f=440:b=4 -b:v 1M -b:a 192k -shortest output-testsrc.mp4

  ffmpeg -f lavfi -i testsrc2=d=60:s=1920x1080:r=24,format=yuv420p -f lavfi -i sine=f=440:b=4 -b:v 1M -b:a 192k -shortest output-testsrc.mp4

  ffmpeg -f lavfi -i smptebars=d=60:s=1920x1080:r=24,format=yuv420p -f lavfi -i sine=f=440:b=4 -b:v 1M -b:a 192k -shortest output-smptebars.mp4

    $cat ~/bin/ffmpeg_grab_desktop.sh
    #!/bin/bash

    size=${1:-"1920x1080"}
    offset=${2:-"0,0"}
    name=${3:-"video"}

    ffmpeg -video_size $size -framerate 25 -f x11grab -i :0.0+$offset -c:v libx264 -crf 0 -preset ultrafast "$name.mkv"
    ffmpeg -i "$name.mkv" -movflags faststart -pix_fmt yuv420p "$name.mp4"

# H264

    $ ffmpeg -i input.avi -c copy -c:v libx264 -crf 18 -preset slow output.mkv

    -c:v libx265 -crf 22

    $ ffmpeg -i input.mkv -i input.srt -map 0 -map 1 -c copy output.mkv

    $ ls *.mkv > mylist.txt
    $ vim mylist.txt # append each line with "file "
    $ ffmpeg -f concat -i mylist.txt -c copy merged-pre-subbed.mkv

     $ ffmpeg -analyzeduration 2147483647 -probesize 2147483647 ...

    -vf yadif

    ffmpeg -i foo.avi -i commentary.mp3 -map 0 -map 1 -c:a copy -c:v libx264 -crf 18 -preset fast  -metadata:s:a:1 title="Commentary" -metadata:s:a:0 language=eng  funk.mkv

    $ ffplay -i foo.mkv -vf "cropdetect=24:16:0"

    <let it run for a minute>

    [Parsed_cropdetect_0 @ 0x7ff093c65c00] x1:0 x2:1919 y1:132 y2:947 w:1920 h:816 x:0 y:132 pts:30155 t:30.155000 crop=1920:816:0:132

    -filter:v:0 "crop=1920:816:0:132"

  # Example output file.
  f=/tmp/output.mp4

  # Example video resolution.
  g=1920x1080

  # Example capture framerate
  fr=4

  # Example X11 display
  d=$DISPLAY

  # Simple screencast.
  #
  # Try adjusting the libx264 CRF from 15 to some greater number, as long
  # as there is no visible effect on video quality.
  #
  # If increasing the capture framerate, you may also wish to use a
  # faster preset.
  ffmpeg  -probesize 50M  -f x11grab -video_size "$g" -framerate "$fr" -i "$d"    \
         -c:v libx264 -crf 15 -preset veryslow   "$f"

  # Simple screencast without drawing the pointer/cursor.
  ffmpeg  -probesize 50M  -f x11grab -video_size "$g" -framerate "$fr" -draw_mouse 0 -i "$d"      \
         -c:v libx264 -crf 15 -preset veryslow   "$f"

  # See what devices are available for capturing sound.
  arecord -l

  # Select a device.
  audioCaptureDevice=hw:0

  # List some permitted parameters associated with device 0.
  #
  # We are interested in the "FORMAT", "CHANNELS", and "RATE" parameters
  # for use in the ffmpeg command.
  arecord --dump-hw-params -D "$audioCaptureDevice"

  audioSampleFormat=pcm_s32le
  audioNumChannels=2
  audioRate=44100

  f=/tmp/output.mp3

  # Record sound.
  ffmpeg  -thread_queue_size 8192 -f alsa -channels "$audioNumChannels" -sample_rate "$audioRate" \
         -c:a "$audioSampleFormat" -ar "$audioRate" -i "$audioCaptureDevice" "$f"

  f=/tmp/output.mkv

  # Screencast with sound.
  #
  # Note that there seems to be an FFMPEG bug where the audio in the last
  # 15 seconds of the video is cut off. The workaround is to record for
  # 15 exrtra seconds, and then cut the extra video.
  ffmpeg  -probesize 50M  -f x11grab -video_size "$g" -framerate "$fr" -i "$d"                    \
         -thread_queue_size 8192 -f alsa -channels "$audioNumChannels" -sample_rate "$audioRate" \
         -c:a "$audioSampleFormat" -ar "$audioRate" -i "$audioCaptureDevice"                     \
         -c:a flac -c:v libx264 -crf 17          "$f"

  Convert AVI to MP4
  ----------------------------
  ffmpeg -i input.avi -c:v libx264 -crf 19 -preset slow -c:a libvo_aacenc -b:a 192k -ac 2 out.mp4

  Convert MP4 to GIF
  ---------------------------
  mkdir frames
  ffmpeg -i video.mp4  -r 5 'frames/frame-%03d.jpg'
  cd frames
  convert -delay 20 -loop 0 -layers Optimize *.jpg myimage.gif

ffmpeg -i snow.mp4 -c:v libx265 -preset slow -crf 28 -tag:v hvc1 -c:a aac -ac 2 -b:a 128k -vf scale=1280:-1 snow.mov

# Merge video from one file, audio from another, trimmed

ffmpeg -i video.mp4 -i audio.mp4 -c:v copy -c:a aac -map 0:v:0 -map 1:a:0 -to 00:00:41 merged.mp4

# Trim a video

ffmpeg -ss 00:06:58 -to 00:08:26 -i TeSiJmLoJd0.webm bbf.mp4

  ffmpeg -i input.mp4 -vf "drawtext=fontfile=font.ttf: text=%{n}: x=48: y=48: fontcolor=white: box=1: boxcolor=0x00000099: fontsize=72" -y output.mp4

  ffmpeg -i input.mp4 -c copy -an output.mp4

    ffmpeg -i $1 -vf scale=320:-1:flags=lanczos,fps=10 /tmp/frames/ffout%03d.png
    convert -loop 0 /tmp/frames/ffout*.png $1.gif

    parallel-moreutils -i -j$(nproc) ffmpeg -i {} -qscale:a 0 {}.mp3 -- ./*.flac
    rename .flac.mp3 .mp3 ./*.mp3

    TIMESTAMP=`date +"%Y-%m-%d_%H"`
    TMP_AVI=$(mktemp /tmp/outXXXXXXXXXX.avi)
    ffcast -s % ffmpeg -y -f x11grab -show_region 1 -framerate 15 \
    -video_size %s -i %D+%c -codec:v huffyuv                  \
    -vf crop="iw-mod(iw\\,2):ih-mod(ih\\,2)" $TMP_AVI         \
    && convert -set delay 10 -layers Optimize $TMP_AVI /home/nemo/Desktop/GIFs/$TIMESTAMP.gif

split-by-audible[1] to split a audiobook from Audible to multiple files by chapters using the copied timestamps from the Audible Web Player.

split-by-silence[2] to split audiobooks by Silence instead

audiobook2video[3] to generate a video file from audiobooks. Puts up a nice cover.

[0]:https://github.com/captn3m0/Scripts/blob/master/split-audio-...

[1]: https://github.com/captn3m0/Scripts/blob/master/split-by-aud...

[2]: https://github.com/captn3m0/Scripts/blob/master/split-by-sil...

[3]: https://github.com/captn3m0/Scripts/blob/master/audiobook2vi...

Example: Start at 52 seconds, take 10 minutes after that:

  ffmpeg -ss 52 -i input.mp4 -c copy -t 00:10:00.0 output.mp4

    ffmpeg -i foo.mp4 -c:v h264_videotoolbox -b:v 1600k foo_out.mp4

To screen capture every 600 frames:

  ffmpeg -i my_vid.mp4 -vf "select=not(mod(n\,600))" -vsync vfr -q:v 15 img_%03d.jpg

  for d in \*
  do
      (montage -mode concatenate -tile 4x -resize 1024x $d"/\* "$d".jpg)
  done

ffmpeg -r 1 -loop 1 -i 1.png -i 1.wav -c:v libvpx -c:a libvorbis -b:a 64k -shortest out.webm (clearly this is old)

-max_muxing_queue_size 2048 (magically fixes some errors and microscopically increases quality, a no-brainer on machines with more than token amounts of RAM)

Every damn time I have to export from after effects and need a file I can actually open.

The original audio files of the dub were at this point still available on archive.org. The problem is that the second audio file is not meant to play directly after the first - this was back in the days of CD players, so halfway through the movie the dub instructs you to begin playing the second CD once the next scene starts. The other problem is that the second file is louder than the first.

Most sources I saw online said to insert a gap of three seconds to account for the delay, and didn’t have a solution for the difference in volume. I wanted to be more precise.

First, I found the exact start time of the scene where the second audio track begins:

    ffprobe hp.mkv
    ...
        Chapter #0:18: start  4428.882000, end 4817.521000
        Metadata:
          title           : Chapter 19
    ...

    ffprobe wiz1.mp3
    ...
      Duration: 01:13:45.33, start: 0.000000, bitrate: 66 kb/s
    ...

I then compared the maximum audio levels of the two audio tracks to determine the level to increase the first track’s volume by (there are more advanced features in FFmpeg for volume normalization, but I just wanted to remove the potential for eardrum damage when beginning Chapter 19 and keep things as similar as possible otherwise):

    ffmpeg -i wiz1.mp3 -af volumedetect -f null -
    [Parsed_volumedetect_0 @ 000001ecf871c1c0] max_volume: -11.1 dB

    ffmpeg -i wiz2.mp3 -af volumedetect -f null -
    [Parsed_volumedetect_0 @ 000001858b881880] max_volume: -3.6 dB

Once I had these numbers, it was time for the one-liner to adjust the first track’s volume, concatenate the two tracks with the gap of silence, and mux them with the video from the movie:

    ffmpeg -i hp.mkv -i wiz1.mp3 -i wiz2.mp3 -filter_complex "[1]volume=7.5dB[wiz1];aevalsrc=0:duration=3.582:sample_rate=22050[gap];[wiz1][gap][2]concat=n=3:v=0:a=1,apad[wiz]" -map 0 -map "[wiz]" -shortest -c:v copy -c:a flac -sample_fmt s16 -f matroska wiz.mkv

  for i in *.webm ; do echo "$i";ffmpeg -i "$i" -acodec copy -vn "${i%.*}.opus" ; done

    ffmpeg -i input.mov -vf "fps=10,scale=600:-1:flags=lanczos,split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse" -loop 0 output.gif

ffmpeg -i ${1} -sn -an -c:v libx264 -r 24 -filter:v "setpts=10PTS" -crf 19 ${1}-10x.mkv

reverse video

ffmpeg -i $IFILE -s 3840x2160 -f image2 -q:v 1 -vf format=yuvj420p $tmpdir/p%8d.jpg cat $(ls -t $tmpdir/p.jpg) | ffmpeg -f image2pipe -c:v mjpeg -r 30 -i - -c:v libx264 -crf 18 -vf format=yuv420p -preset slow -f mp4 $OFILE

loop a video: loopcount=$1

ffmpeg -stream_loop $1 -i $2 -c copy $3.mkv

https://www.fileformat.info/format/mspaint/egff.htm

Assuming that you actually meant video content, I think your question may be a bit misguided on the nuances and goals of video encoding. Video encoding can be both lossy and lossless. Lossless video encoding isn't particularly interesting in most cases, but I do believe that HEVC (H.265) will usually come out slightly smaller. However anything to do with encoding will always vary based on the actual source content. So partial answer to your question would probably be x265, but it depends. Based on the source you could construct theoretical content that could be better tuned to one or the other's encoding strengths.

Where it gets interesting is in lossy encoding. With lossy encoding you seek to retain visual acuity to a certain standard while minimizing size and/or processing requirements. Both codecs do an excellent job at removing the right amount of information to effectively fool the human observer. With lossy encoding there isn't really a filesize difference, as you tune your filesize to whatever you want to given your source and your desired output constraints. The big feature of av1 is that it is open and unencumbered by patents+royalties and will hopefully therefore make it THE industry standard in the coming years. It's openness also makes it more likely to eventually be ubiquitous as it should be implementable and playable on most new video platforms and hardware, and hopefully the mythical one format that just works everywhere.

    AV1    100 MiB
    H.265  500 MiB
    H.264  1.5 GiB

In non-animated content, the difference is less impressive, but comes at about ~20% in favor of AV1 vs HEVC, in my subjective-and-not-rigorously-benchmarked opinion. But "video quality" is subjective anyway.