BestSource (abbreviated as BS) is a cross-platform wrapper library around FFmpeg that ensures sample/frame accurate access to audio and video by always linearly decoding the input files. With a few tricks this can guarantee accurate "seeking" and can be surprisingly... not slow.
It can be used as either a C++ library directly or through the VapourSynth plugin that's included.
Requires FFmpeg, Jansson and libp2p to compile.
bs.AudioSource(string source[, int track = -1, int adjustdelay = -1, int threads = 0, bint exact = True, bint enable_drefs = False, bint use_absolute_path = False, float drc_scale = 0, string cachepath, int cachesize = 100, bint showprogress = True])
bs.VideoSource(string source[, int track = -1, bint variableformat = False, int threads = 0, int seekpreroll = 20, bint exact = True, bint enable_drefs = False, bint use_absolute_path = False, string cachepath, int cachesize = 1000, string hwdevice, bint showprogress = True])
track: Either a positive number starting from 0 specifying the absolute track number or a negative number to select the nth audio or video track. Throws an error on wrong type or no matching track.
adjustdelay: Adjust audio start time relative to track number. Pass -2 to disable and -1 to be relative to the first video track if one exists.
variableformat: Allow format changes in the output for video. Untested.
threads: Number of threads to use for decoding. Pass 0 to autodetect.
seekpreroll: Number of frames before the requested frame to cache when seeking.
exact: Decode the full track to get an exact frame/sample count. Will throw an error if set to false and the frame or sample count can't be guessed at all. If too many frames/samples is guessed the end is passed with the last available frame/silence to fill up the missing data.
enable_drefs: Option passed to the FFmpeg mov demuxer.
use_absolute_path: Option passed to the FFmpeg mov demuxer.
drc_scale: Apply dynamic range compression to ac3 audio. 0 = None and 1.0 = Normal.
cachepath: The full path to the cache file. Defaults to %LOCALAPPDATA%\bsindex.json or ~/bsindex.json depending on the OS.
cachesize: Maximum internal cache size in MB.
hwdevice: The interface to use for hardware decoding. Depends on OS and hardware. On windows d3d11va and cuda are probably the ones most likely to work. Defaults to CPU decoding. Will throw errors for formats where hardware decoding isn't possible.
showprogress: Print indexing progress as VapourSynth information level log messages when exact frame/sample count is determined.
bs.SetLogLevel(int level)
bs.GetLogLevel()
Sets the log level of the FFmpeg library. By default quiet. See FFmpeg documentation for allowed constants. Both functions return the current/newly set level. Mostly useful for debugging purposes.