How to burn ass subtitle into (mpeg-1/2 (mpgv)) with best quality?

[parumaru]

I have this particular MKV file and its details are in the pic below.



Now I want to convert it to MP4 and hard-code the ass subtitle into it.

I know that I can't avoid re-encoding the video(?) by using

-c:v copy

in ffmpeg, so I was wondering if there is anyway to best preserve the quality of the video?

I don't mind the problem of the file size, since it is a 1-2 minute video anyway.

Some suggestion is to make a lossless video, so I did

ffmpeg -i "input.mkv" -preset veryslow -crf 0 -c:a aac -vf "ass=sub.ass" "output.mp4"

This does work (even though the file is 3 times the original), but still
the quality was not as good as the original and the colour is slightly brighter.

Hence, I am curious if there are more ways to do this?

[sneaker]

the quality was not as good as the original and the colour is slightly brighter.

That isn't really possible. x264 lossless mode is 100% lossless. Maybe it's a playback problem. Or are you talking about subtitle quality/color?

Provide sample files, ffmpeg log and screenshots showing the problem.

[parumaru]

@sneaker Thank you so much for such a quick reply.
Oh so if I already specified -preset veryslow -crf 0, the video should be exactly the same?
Am I understanding correct?

As you can see, the subtitle on Aegisub looks quite sharper and has slightly better colour.
The difference is very slightly, but I'm just curious if there is a way to make it better?

[sneaker]

I don't know from the top of my head but it could be in Aegisub the subtitles are without chroma-subsampling (4:4:4) while your video is not (4:2:0 / yuv420p). To achieve the same sharpness you'd need to upscale at least the chroma. (see ffmpeg pixel formats)

[parumaru]

x264 lossless mode is 100% lossless.

@sneaker

May I ask you to elaborate more about this part?

When you say x264 lossless mode, did you mean setting -preset veryslow -crf 0 that I did?

and 100% lossless -> Does this mean the video should be 100% like the original?

[sneaker]

Assuming you are using x264 8 bit (like is usually the case): yes.

[parumaru]

Assuming you are using x264 8 bit (like is usually the case): yes.

Ohh sorrry I forgot to specify that

yes I believe I'm using x264 (not sure about the bit though) as vcodec is now H264-MPEG-4 AVC(part 10) (avc1)?