logged

The error lines FFmpeg logged on the failing call's thread while it ran, oldest first (#170).

FFmpeg's return code says what kind of failure it was, and its log says why: a cut-off MP4 fails with FFmpegError.InvalidData while the MP4 reader logs moov atom not found, and an encoder refuses a sample rate with FFmpegError.InvalidArgument while it logs the rates it takes. The calls that open or set something up collect these lines whether or not a log sink is installed, and a sink still receives each of them as usual: opening a MediaSource and reading its stream info, opening a decoder, a subtitle decoder or an encoder, writing a MediaSink's header, and building a FilterGraph. When one of them fails, its exception carries the lines here and its message ends with them.

Only lines at FFmpegLogLevel.Error or more severe are kept, at most 8 of them, and only those logged on the thread that made the call, so a line another call logs at the same moment on another thread never lands here. Empty when FFmpeg logged nothing, which is common: a file no reader recognises fails with FFmpegError.InvalidData and no line at all, and empty for every failure of a call that does not collect lines, such as a packet read.