maximum interval between keyframes in frames (default: 250 or one keyframe every ten seconds in a 25fps movie. This is the recommended default for MPEG-4). Most codecs require regular keyframes in order to limit the accumulation of mismatch error. Keyframes are also needed for seeking, as seeking is only possible to a keyframe − but keyframes need more space than other frames, so larger numbers here mean slightly smaller files but less precise seeking. 0 is equivalent to 1, which makes every frame a keyframe. Values >300 are not recommended as the quality might be bad depending upon decoder, encoder and luck. It is common for MPEG-1/2 to use values <=30.
1 - Not recommended (much larger file, little quality difference and weird side effects: msmpeg4, h263 will be very low quality, ratecontrol will be confused resulting in lower quality and some decoders will not be able to decode it).
2 - Recommended for normal mpeg4/mpeg1video encoding (default).
3 - Recommended for h263(p)/msmpeg4. The reason for preferring 3 over 2 is that 2 could lead to overflows. (This will be fixed for h263(p) by changing the quantizer per MB in the future, msmpeg4 cannot be fixed as it does not support that.)
Maximum quantizer, 10−31 should be a sane range (default: 31).
Constant quantizer / constant quality encoding (selects fixed quantizer mode). A lower value means better quality but larger files (default: −1). In case of snow codec, value 0 means lossless encoding. Since the other codecs do not support this, vqscale=0 will have an undefined effect. 1 is not recommended (see vqmin for details).
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