Encoder buffer model
When using the x264 system output, bitrate can be controlled using VBV (Video Buffer Verifier). VBV is a theoretical MPEG video buffer model used to ensure that an encoded video stream can be correctly buffered and played back at the decoder device. By definition, the VBV should not overflow or underflow when its input is a compliant stream. When encoding such a stream, it is important that it complies with the VBV requirements. There are two parameters that need to be set for VBV controls — VBV buffer size and VBV maximum bitrate. Consider a small time period T over that desired to restrict the data throughput. We recommend a VBV buffer size of 1-5x video bitrate, and all renditions use the same VBV buffer size multiplier:
- VBV buffer duration = VBV buffer size / VBV maximum bitrate
- VBV data throughput = (T + VBV buffer duration) * VBV maximum bitrate
It is important to keep VBV data throughput well below the video maximum bitrate specification of the highest H.264 profile the device can support and the average net- work bandwidth available for video of end user.