New answers tagged conversion
An MP4 file normally contains H.264 video and AAC audio, both of which are compatible with the FLV container. You could simply copy over the streams: ffmpeg -i input.mp4 -c copy output.flv Since you're copying the streams, this will be as close to instantaneous as you're going to get and will not result in any loss of quality.
Because 4096 / 1920 = 2.13333 and 2160/1080 = 2. They are different aspect ratios, so yes, they end up letter boxing when you convert between them. That is the expected result. The 4K format you are using is a multiple of 2K and is not the same widescreen aspect ratio as 1080p. You can't translate between them without letterboxing, though there are ...
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