IVF容器格式
Extension: ivf
IVF is a simple file format that transports raw VP8 data.
An IVF file begins with a 32-byte header.
The header is followed by a series of frames. Each frame consists of a 12-byte header followed by data.
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IVF容器的后缀名是.ivf.
用来封装vp8或vp9数据.
其文件头32字节，头之后是一帧一帧数据，帧数据的开头是12字节的帧头。
File Header(32 Bytes)
bytes 0-3 signature: 'DKIF'
bytes 4-5 version (should be 0)
bytes 6-7 length of header in bytes
bytes 8-11 codec FourCC (e.g., 'VP80')
bytes 12-13 width in pixels
bytes 14-15 height in pixels
bytes 16-19 frame rate
bytes 20-23 time scale
bytes 24-27 number of frames in file
bytes 28-31 unused
举例:
Frame Header(12 Bytes)
bytes 0-3 size of frame in bytes (not including the 12-byte header)
bytes 4-11 64-bit presentation timestamp
muxing overhead of IVF
假设ivf文件的大小为ivf_mux_size字节，其中的数据为frame_count帧，那么muxing overhead是多少?
overhead_size = 32 + 12 * frame_count
raw_data_size = ivf_mux_size - overhead_size
muxing_overhead = overhead_size/raw_data_size
