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+--- Thread: [INFO] Bitrate settings (/thread-3860.html)
Bitrate settings - zspeciman - 07.09.2024
I'm trying to get a better understanding regarding Bitrate settings:
If the source video is 1000kbps 640x480 25fps black & white mp4 video, and I colorize the clip with Deoldify, do I have to increase the bitrate to accommodate for the color? If so what would be a good bitrate?
If I upscale the same (now colorized) video to 1920x1080 (letter box), what would be the recommended bitrate?
If I use rife 2x (now colorized and upscaled) video, what would be the recommended bitrate?
RE: Bitrate settings - Selur - 07.09.2024
Okay,... first problem I have is that bit rate sadly does not say anything about the amount of details or the quality of the source.
Also, I would not use bitrate, but quality based encoding.
(with vbv I see no real point in using bit rate based encoding unless you need to hit a specific file size and the the question about bit rate is answered by the target size)
That said, for the sake of argument, let's assume the source was optimally compressed, and re-encoding the source would also be optimally done.
Quote:If the source video is 1000kbps 640x480 25fps black & white mp4 video, and I colorize the clip with Deoldify, do I have to increase the bitrate to accommodate for the color?Assuming your source has no chroma info and thus effectively is 4:0:0 YUV content, just be adding color you have more information:
4:0:0: Only luma information is stored and(Y: 8 bits, U: 0 bits, V: 0 bits) requires 8 bits per pixel
4:2:0: Chroma subsampled both horizontally and vertically by 2 (Y: 8 bits, U: 2 bits (averaged over 4 pixels), V: 2 bits (averaged over 4 pixels)) and requires 12 bits per pixel.
4:2:2: Chroma subsampled horizontally by 2 (Y: 8 bits, U: 4 bits (averaged over 2 pixels), V: 4 bits (averaged over 2 pixels)) and requires 16bits per pixel.
4:4:4: Full chroma and luma information for each pixel(Y: 8 bits, U: 8 bits, V: 8 bits) and requires 24 bits per pixel.
So without compression, going from 4:0:0 to 4:2:0 would increase the amount of data by 50%.
Depending on the target format the used and encoder and its settings, the actually needed data, i.e. when compressing losslessly should be way lower.
(my gut feeling, for a modern lossy encoder&format maybe 10%)
Quote:If I upscale the same (now colorized) video to 1920x1080 (letter box), what would be the recommended bitrate?Going from 640x480 to 1920x1080 would increase the number of by a factor of 6.75, but since you usually don't have that much more information in a 1920x1080 source, I would suspect more like a factor of 3.5 to 5 on natural content. (will be way less on cartoons&co)
Quote:If I use rife 2x (now colorized and upscaled) video, what would be the recommended bitrate?Increasing the frame rate and by a factor of 2 in theory would add 2 times the amount of information. But the actual gain in information is way less, so I would probably expect an increase of maybe 20% of needed the required output size / bit rate.
=> I would not advise using bitrate based encoding, but if you want/must, hopefully the above helps a bit about the general.
Cu Selur
Ps.: if you used lossless intraframe only, compression the increases would be higher, since basically no motion compensation (basic MPEG ideal) would be used.
RE: Bitrate settings - zspeciman - 07.09.2024
Thank you for the quick reply and explanation.
The black & white source is 4:2:0. Advanced Video Coding, Main@L3.1 CABAC / 4 Ref Frames. In that case, would that need more data going to color?
Does going 4x3 to 16x9 letterbox same resolution (just adding black bars to the left and right) require more data or is it negligible, because the black bars doesn't require much data?
So for a 1000kbps 4:2:0 640x480 25fps to 1920x1080 letterbox 50fps mp4, a 5000kbps would be a good target? (using average bitrate 1st pass)
Final question. Does setting the target at 5000kbps require more or less computation time than 2500kbps or its the same?
RE: Bitrate settings - Selur - 07.09.2024
Quote: The black & white source is 4:2:0. Advanced Video Coding, Main@L3.1 CABAC / 4 Ref Frames. In that case, would that need more data going to color?If you look at the Vapoursynth Preview with split YUV ('Compare view' enabled, 'Filtering->Vapoursynth->Misc->Preview->Split Compare View' enabled and set to 'splitYUV&interleaved' (or just 'interleaved') ), this way you can see what happens in the chroma.
If the black&white has no chroma data it's basically 4:0:0 an modern encoders will nearly drop the chroma planes, thus when you add data chroma is will need to be compressed.
Quote:Does going 4x3 to 16x9 letterbox same resolution (just adding black bars to the left and right) require more data or is it negligible, because the black bars doesn't require much data?black bars should be negligible (especially if they are at macroblock / mod16 borders)
Quote:So for a 1000kbps 4:2:0 640x480 25fps to 1920x1080 letterbox 50fps mp4, a 5000kbps would be a good target? (using average bitrate 1st pass)Just reading 'average bitrate 1pass' I would say: No, using 1pass bitrate encoding is a dumb thing.
But assuming the amount of details scales with the pixel density, it should produce similar quality.
Instead of guessing bit rates, I would recommend doing a few 1 pass crf encodes (16-23) and see what prefers the quality level you need.
Quote:Final question. Does setting the target at 5000kbps require more or less computation time than 2500kbps or its the same?More, assuming CABAC or similar encoding methods are used, which all newer formats do.
Cu Selur