Record A/V uses 4:4:4 chroma subsampling with lossless

[felixjones]

I've noticed this a few times now and it's quite an inconvenience for recording videos in lossless.
The use of 4:4:4 chroma means many video players will fail to play lossless videos recorded in mGBA (web players in particular).

This makes mGBA lossless recorded videos difficult to share over Twitter, Discord and more.

At 240x160 4:4:4 lossless is probably desirable, but at 2x resolution and greater then 4:2:0 should suffice.

In my opinion, let 4:2:0 be the default for lossless and force the encoding resolution to be 2x sized and move 4:4:4 into the advanced settings.

[pinobatch]

Web browsers prefer 4:2:0, which means one pair of chroma (UV) samples for each 2x2 block of pixels. This can be done without quality loss by doubling all pixels before encoding. For example, this FFmpeg command converts video to the YUV 4:2:0 space that video players inside web browsers and consumer electronics devices (such as tablets and phones) prefer:

ffmpeg -y -i "game_444.avi" -i "game.wav" \
  -vf 'scale=480:320:sws_flags=neighbor' \
  -pix_fmt yuv420p -ab 128000 -movflags +faststart "out.mp4"

(This is adapted from a bgb encoding tutorial that I wrote for Libbet and the Magic Floor.)

If I had my way, I'd default to pixel-doubled 4:2:0 if a lossy codec is chosen or 4:4:4 with a lossless codec (zmbv, lagarith, etc.).

[felixjones]

I spent a couple minutes checking out the other options. Seems like the lossless preset forces 4:4:4, the other presets (YouTube, etc) use 4:2:0 correctly.

I've updated this issue to reflect that lossless not working on web players still isn't very friendly. 4:4:4 should be moved to the advanced section and lossless recorders at atleast 2x resolution by default.
I expect the casual user (like myself) will select lossless expecting best quality, but then be surprised that it does not play on Discord and is rejected by Twitter.

This is one of those subtle user errors.

[endrift]

Many video players don't support lossless H.264 anyway. And if I'm not using 4:4:4 it's not lossless anyway. This is a usability concern at best.

[pinobatch]

Is there room for a warning that a lossless encode is unlikely to play on web browsers or consumer electronics devices?