ffmpeg

Use ffmpeg with -movflags faststart, -pix_fmt yuv420p, and a scale filter forcing even dimensions: ffmpeg -i input.gif -movflags faststart -pix_fmt yuv420p -vf "scale=trunc(iw/2)*2:trunc(ih/2)*2" output.mp4. This ensures browser compatibility and valid codec dimensions.

Use filter_complex combining setpts for video and atempo for audio, for example setpts=0.5*PTS with atempo=2.0 for 2x speed. For speeds above 2x, chain multiple atempo filters since each is limited to the 0.5-2.0 range.

Use Remotion playbackRate for simple constant speeds, but use FFmpeg preprocessing for extreme speeds above 4x, variable speed changes, or when fitting a demo to exact voiceover timing. Remotion playbackRate must be constant and cannot interpolate over frames.

The H.264 codec requires even width and height dimensions, so odd input resolutions cause this error. Fix it by adding a scale filter: -vf "scale=trunc(iw/2)*2:trunc(ih/2)*2" to round dimensions down to even values.

CRF 23 is the default for general use; use 18 for archive masters, 20-22 for production, 23-25 for web delivery, and 28 or higher for quick drafts. Lower CRF means better quality and larger files.

Twitter limits videos to 140 seconds, 512MB, and 1920x1200 resolution. Export with libx264 at CRF 24, scale to at most 1280x720, AAC audio at 128k and 44.1kHz, and add -movflags +faststart for reliable upload and playback.