callback to negotiate the pixelFormat
@param fmt is the list of formats which are supported by the codec,
it is terminated by -1 as 0 is a valid format, the formats are ordered by quality.
The first is always the native one.
@note The callback may be called again immediately if initialization for
the selected (hardware-accelerated) pixel format failed.
@warning Behavior is undefined if the callback returns a value not
in the fmt list of formats.
@return the chosen format
- encoding: unused
- decoding: Set by user, if not set the native format will be chosen.
callback to negotiate the pixelFormat @param fmt is the list of formats which are supported by the codec, it is terminated by -1 as 0 is a valid format, the formats are ordered by quality. The first is always the native one. @note The callback may be called again immediately if initialization for the selected (hardware-accelerated) pixel format failed. @warning Behavior is undefined if the callback returns a value not in the fmt list of formats. @return the chosen format - encoding: unused - decoding: Set by user, if not set the native format will be chosen.