H.264 H.265 一些知識
H.264/AVC
H.265/HEVC 高效率視訊編碼（High Efficiency Video Coding，簡稱HEVC）
stackoverflow 上ffmpeg 轉碼命令：
https://stackoverflow.com/questions/58742765/convert-videos-from-264-to-265-hevc-with-ffmpeg
Convert 4k to 1080 (no change in codec)
ffmpeg -i input4kvid.mp4 -vf scale=1920:1080 -c:a copy output1080vid.mp4
Convert h.264 to h.265 (no change in resolution)
ffmpeg -i input.mp4 -c:v libx265 -vtag hvc1 -c:a copy output.mp4
Convert 4k(h.264) to 1080(h.265)
Downscaling + Change in compression codec
ffmpeg -i input.mp4 -c:v libx265 -vtag hvc1 -vf scale=1920:1080 -crf 20 -c:a copy output.mp4
Options Explained
-i input file name or file path
-c:v libx265 -vtag hvc1 selecting compression. Default is libx264
-vf scale=1920:1080 specifying output resolution
-c:a copy copy audio as it is without any compression
-preset slow ask compression algorithm to take more time & look for more areas for compression. Default is medium. Other options are faster, fast, medium, slow, slower
-crf 20 Compression quality
-crf 0 high-quality, low compression, large file
-crf 23 default
-crf 51 low-quality, high compression, small file
-vtag hvc1 use codec hvc1 (a.k.a. HEVC or h.265) during conversion.
If -vtag isn't specified (like in the first snippet), it will then use the codec used in the src file.
Web端H.265播放器研發解密