Upload spec
Watch as an animation →Match the format a platform or contest accepts, to prevent rejection and quality loss.
Just before final export, and before submitting to a contest.
Follow the contest rules first (for example, one contest required 1 minute or less, 16:9 at 1920×1080 or larger, MP4/MOV, and public visibility as a regular video). YouTube recommends MP4 (moov atom at the front), H.264 High profile, progressive, 4:2:0, the same frame rate as the source, AAC-LC at 48 kHz (384 kbps recommended for stereo), and BT.709 for SDR. Seedance output is HEVC, so re-encode to H.264 for submission. Before joining, set the sample rate of all audio to one value with aresample=48000 (YouTube recommends 48 kHz). Make the thumbnail a 16:9 JPG or PNG. YouTube's recommended resolution is 3840×2160 (minimum width 640px), and the size limit is 2 MB for phone uploads and 50 MB for PC uploads. If there are realistic scenes made with AI, choose Yes for "Altered or synthetic content" on the upload screen. For the last check, use ffprobe -v error -show_entries format=duration,size:stream=width,height,codec_name -of default=nw=1 input.mp4.
Re-encode for upload as H.264 High profile MP4 with 48 kHz AAC audio and the header first: ffmpeg -i in.mp4 -c:v libx264 -profile:v high -pix_fmt yuv420p -crf 17 -c:a aac -b:a 384k -ar 48000 -movflags +faststart out.mp4. Always follow the contest or platform rules first, and make a 1280x720 JPG thumbnail under 2 MB.