With the raw bitstream method example from above, there is no need for a complex filtergraph. Using a complex filtergraph, you can speed up video and audio at the same time:įfmpeg -i input.mkv -filter_complex "setpts=0.5*PTS atempo=2.0" -map "" -map "" output.mkv The following with quadruple the audio speed:įfmpeg -i input.mkv -filter:a "atempo=2.0,atempo=2.0" -vn output.mkv If you need to, you can get around this limitation by stringing multiple atempo filters together.
The atempo filter is limited to using values between 0.5 and 2.0 (so it can slow it down to no less than half the original speed, and speed up to no more than double the input). To double the speed of audio:įfmpeg -i input.mkv -filter:a "atempo=2.0" -vn output.mkv You can speed up or slow down audio with the atempo audio filter. Other options include slowmoVideo and Butterflow. This is also known as "motion interpolation" or "optical flow".įfmpeg -i input.mkv -filter:v "minterpolate='mi_mode=mci:mc_mode=aobmc:vsbmc=1:fps=120'" output.mkv You can smooth out slow/fast video with the minterpolate video filter. To slow down your video, you have to use a multiplier greater than 1:įfmpeg -i input.mkv -filter:v "setpts=2.0*PTS" output.mkv For example, to go from an input of 4 FPS to one that is sped up to 4x that (16 FPS):įfmpeg -i input.mkv -r 16 -filter:v "setpts=0.25*PTS" output.mkv You can avoid dropped frames by specifying a higher output frame rate than the input. Note that this method will drop frames to achieve the desired speed. For example, if there are two succesive frames shown at timestamps 1 and 2, and you want to speed up the video, those timestamps need to become 0.5 and 1, respectively. The filter works by changing the presentation timestamp (PTS) of each video frame. To double the speed of the video with the setpts filter, you can use:įfmpeg -i input.mkv -filter:v "setpts=0.5*PTS" output.mkv Then generate new timestamps while muxing to a container:įfmpeg -fflags +genpts -r 30 -i raw.h264 -c:v copy output.mp4Ĭhange the value of -r to the desired playback frame rate. Use this if you require no other changes to your input video.įirst, copy the video to a raw bitstream format.įfmpeg -i input.mp4 -map 0:v -c:v copy -bsf:v h264_mp4toannexb raw.h264įfmpeg -i input.mp4 -map 0:v -c:v copy -bsf:v hevc_mp4toannexb raw.h265 This method is lossless and apart from changing the timestamps, copies the video stream as-is.
Note that in the following examples, the audio stream is not changed, so it should ideally be disabled with -an. This can be done via two methods: using the setpts video filter (which requires re-encoding) or by erasing the timestamps by exporting the video to a raw bitstream format and muxing to a container while creating new timestamps. However, it is primarily and more directly related to molecular speed and thus temperature than it is to anything else.The speed of a video stream can be changed by changing the presentation timestamp (PTS) of each video frame. One might also note that the temperature is lower as one ascends primarily because the pressure is lower as one ascends and then conclude that the speed difference is equally attributable to lower pressure (or lower density for that matter). Since molecular speed in a gas is a direct function of average molecular kinetic energy and that is a direct function of temperature, the speed of sound in a gas will also be a function of temperature.Īt the cruise altitude of the Concorde the atmospheric temperature is below that of the standard atmospheric temperature at sea level, so the speed of sound is also lower. Therefore, the sound wave can not possibly move through the gas at a speed greater than that of the individual molecules themselves, and in fact must move at a lower speed than that due to the random nature of molecular movement. Falcon Ballistics, A division of Falcon Reservoir Engineering Ltd. A sound wave moving through a gas requires a small scale bulk movement of gas molecules back and forth as pressure at any locations builds or falls. Speed of sound (fps) sqrt(2403.2 (Temp + 459.67) ) where I have grouped a number of constants into the value 2403.2 Mach Number velocity / speed of sound Temperature (F) Velocity (fps) Calculate Speed of Sound (fps) Mach Number 2022.
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