@param cmd the command to process, for handling simplicity all commands must be alphanumeric only
@param arg the argument for the command
@param res a buffer with size res_size where the filter(s) can return a response. This must not change when the command is not supported.
@param flags if AVFILTER_CMD_FLAG_FAST is set and the command would be
time consuming then a filter should treat it like an unsupported command
@returns >=0 on success otherwise an error code.
AVERROR(ENOSYS) on unsupported commands
Make the filter instance process a command.
@param cmd the command to process, for handling simplicity all commands must be alphanumeric only @param arg the argument for the command @param res a buffer with size res_size where the filter(s) can return a response. This must not change when the command is not supported. @param flags if AVFILTER_CMD_FLAG_FAST is set and the command would be time consuming then a filter should treat it like an unsupported command
@returns >=0 on success otherwise an error code. AVERROR(ENOSYS) on unsupported commands