Set a video to any custom bitrate in kbps

CBR (Constant Bit Rate) maintains a fixed bitrate regardless of scene complexity — necessary for streaming or delivery specs that require predictable bandwidth (IPTV, broadcast playout, OTT delivery). VBR (Variable Bit Rate) allocates bits where they are needed — more bits to complex scenes, fewer to static scenes — producing better quality at the same average bitrate. For general delivery where a target size is the requirement, VBR with average bitrate targeting is recommended. For streaming playout, CBR is typically required.

Two-pass encoding is the most accurate method for hitting a bitrate target. Pass 1 analyses the full video complexity. Pass 2 allocates bits based on the analysis to meet the target. In practice, two-pass encoding hits the target bitrate within 1–3%, which is within the tolerance of most delivery specifications. Single-pass with -b:v targeting is less accurate and may produce files 5–15% above or below target.

The buffer size (vbv-bufsize) defines how much of the bitrate can vary instantaneously around the target. A larger buffer allows bigger peaks for complex scenes. For streaming (where the player buffer is small), set bufsize equal to the target bitrate for a 1-second buffer. For file delivery (where bitrate variance is acceptable), a 2–4 second buffer is fine. Broadcast specs typically define both the bitrate target and the buffer size explicitly.