Visually lossless 1080p to 720p using ffmpeg

Question

I have an mkvvideo file which is 1080p

Video: hevc (Main 10), yuv420p10le(tv), 1920x1080, SAR 1:1 DAR 16:9, 23.98 fps, 23.98 tbr, 1k tbn, 23.98 tbc (default)

Can someone help me convert it to visually lossless 720p without taking much time. I am ok with whatever file size it comes up. It is a 43 minute video file and is around 800 MB now.

The reason I am doing is 1080p stutter in my old laptop HD screen. When I tried Handbrake, it says ETA is 12 hours. I would prefer FFMPEG this time.

I saw a few other commands, but not sure whether it will work with my video file and FPS. Please do share the proper FFMPEG command for this purpose. Thanks.

Solution

The ultrafast preset option for x264 will make it go as fast as it can:

ffmpeg -i INPUT -c:a copy -c:v libx264 -crf 10 -preset ultrafast -s 1280x720 -pix_fmt yuv420p -map 0 OUTPUT

• -c:a copy will copy audio tracks instead of re-encoding
• -c:v libx264 – use libx264 encoder for video tracks
• -crf 10 value is low enough to look good (even with ultrafast preset), but will produce quite a large file. Changing this up to -crf 18 can result in a file size 2-5x smaller – but depending on content/viewing conditions may not be considered "visually lossless" (a subjective requirement – try different crf values with small samples beforehand by adding e.g. -ss 23:00 -to 23:10 before the input)
• -s 1280x720 resizes the output to 1280x720
• -map 0 will map ALL the streams from the first input into the output file, or use -map 0:v -map 0:a? -map 0:s? to map all video tracks, and all audio/subtitle tracks, if they exist
• If container format used for OUTPUT is mov or mp4, the option -c:s mov_text will encode text-based subtitles

Comments

[Mike Scott]

There’s no such thing as visually lossless downscaling.

[user227495]

I was trying to say as good as possible. Thanks.

[Keltari]

Handbrake uses FFMPEG for its encoding. You might not get much improvement in speed. However, maybe with the right options, you could.

[user227495]

It would be great if you can help with that.

[Daniel B]

If your notebook is incapable of 1080p HEVC playback, it most certainly isn’t fast at encoding it either. You do not mention the settings you tried in Handbrake.

[user227495]

I used fast and very fast for 720p, 30 fps. Everything else was default. I chose Matroska instead of mpv4.

[Admin]

Will produce large files and take a while on a weak cpu: ffmpeg -i INPUT -c copy -c:v libx264 -crf 10 -preset ultrafast -s 1280x720 -pix_fmt yuv420p OUTPUT.mkv, or leave it @ 1920x1080: -crf 7 -preset ultrafast -pix_fmt yuv420p (will be ~2.5-3x larger than 1280x720). If input file is HDR tonemapping may be wanted. Leave the framerate as it is.

[user227495]

If we use h265 or v9, will it make any difference ? I heard it gives better results. Just curious. Thanks.

[user227495]

@guest the first command worked like a charm. Picture and audio quality is good for an HD screen. 800 MB is now around 6.5 GB now, but that is fine. It took only 1 hour 15 minutes. The only regret is that there was subtitle available with the original video. It got lost in this one. If you can post this as an answer and (optionally) a method to keep the subtitle, I can accept it as an answer. Thanks.

[Admin]

@user227495 Sorry I forgot about possibility of subs. It would be possible to remux the subtitles back (without re-doing the x264 encode): ffmpeg -i NEWFILE -i ORIGINALFILE -c copy -map 0 -map 1:s OUTPUT – if output is to mp4 or mov container, add -c:s mov_text before the output file

[user227495]

I got this error -- Stream mapping: Stream #0:2 -> #0:0 (hdmv_pgs_subtitle (pgssub) -> ass (ssa)) Press [q] to stop, [?] for help [ssa @ 0x55fe090e0380] Only SUBTITLE_ASS type supported. Subtitle encoding failed Conversion failed!

[user227495]

Used this command --- ffmpeg -i INPUT.mkv -c:a copy -c:v libx264 -crf 10 -preset ultrafast -s 1280x720 -pix_fmt yuv420p -map 0:s OUTPUT.mkv

[Admin]

Sorry, I don't know much about subs – try replacing -map 0:s with -c:s dvdsub -map 0:v -map 0:a -map 0:s

[user227495]

Thanks. Any idea how to use mkvToolNix ?

[user227495]

Read that it is easy to extract subtitles through it. I don't mind adding subtitle file separately.

[Admin]

Looks like that would be mkvextract INPUT.mkv tracks 2:OUTPUT.sup. The manual says: PGS subtitles will be written as SUP files.

[user227495]

No need to use ffmpeg in the beginning ?

[user227495]

It works. You are awesome. It works even if we use SRT instead of .sup.

[Elisa Cha Cha]

You can likely use -crf 18 and have a ~60% smaller file compared to -crf 10.